Long is unusual for me, just to share another experience. All scan within couple mins.

There have been weird issues for me with TTS-1 this year. Home Studio when I first bought it TTS-1 would not load, grayed out. I totally forget what I did to fix it but it has worked fine since, note I only use 44.1. 
Then on my office computer same thing,  grayed out and not available?? I don't use that computer for recording so haven't bothered to see what's wrong and sorry I can't remember the fix which was probably the RE Scan. .  I use it to download the latest Sonar stuff and then transfer the files to my DAW. TTS-1 has always worked without issue on my main DAW so it's not a corrupted download. 
 
One way to test the crashing issue would be a quick test.
 
Go to preferences MIDI and un check all outputs for midi. 
Now Download any GM Midi file and OPEN it. 
This should load TTS_1 into a fresh project and play the file. 
 
This is the only use I have for TTS_1 is to get a song going, from there I replace everything. The TTs sound quality is less than half of most all other VST's,
example:
You mentioned an upright bass. I agree the TTS_1 upright is not bad, Now open Dim Pro and try the "Full Acoustic" you'll never go back to TTS-1. 
You just need to take a bit of time and explore what we already have. Dim Pro alone blows away TTS-1 and have just about everything. Yes that Air expand pack goes on sale and is a mind boggling supply of great sounds too. 
TTS-1 is a good starting point and I hope Cakewalk looks into the bugs and thinks about updating it. We need a GM multitimbral synth. 

@Msorrel - Thanks, I might take you up on that if this latest info hadn't come to light:
 
I have removed the TTS tracks entirely, and disabled Session Drummer for the time being. I've replaced the TTS tracks with other plug ins, which is ok for now. I've cleaned everything out that was extraneous, such as a few stray synths I wasn't using but were still loading, etc. Now I have been working on the project for about an hour without incident. Woohoo... but it finally did crash, and so I thought I'd try to exactly match my steps to get a repro -- and that was successful. The piece itself for the full orchestra is so far 17 minutes. But the whole project is more like 35 because I have a track called ORIG which is just a single Midi piano containing the piano sketch version of the piece which starts at about 19 minutes. Because I'm adding and removing stuff I can't line up the piano sketch with the real piece, because it wouldn't line up. I do frequent drag-drops from the piano sketch to the full piece. 
 
http://imgur.com/a/JKYbw
Here is a video of my entire load process for this project. (The Play loading progress bars didn't render correctly, it doesn't really look like that.) For those claiming their Play instruments load more quickly, this video shows the project loading in real time. You can also see all the instruments I'm using, how the tracks are laid out, etc. At the end of the video, I cause the project to crash Sonar. I've discovered that I can reliably repro when I move the now time out to about 18 minutes and hit Play. This is after the orchestra stuff is done, but before the piano sketch begins. I can split it into two separate projects, so not a problem. My plan of attack now is to do just that. The first ~17 minutes is the full orchestra, and after that it's the original piano sketch, just a single midi track. 
 
Any idea whether this crash is caused by something in one of the otherwsie-well-behaving tracks? Why would Sonar crash only when the now time is moved to a certain spot?

According to your signature, you're using an M-Audio Delta interface in Windows 10. Did they eventually release Windows 10 drivers for the delta series? Last time I checked for a friend, there were none. If using a legacy driver, this could be a large source of your problems, and might be best to get an interface that is compatible with Windows 10.
 

Oh really? Wouldn't it be awesome if it was something simple as that. I'll look into that, thank you! Anything else anyone sees?
 
Since I posted that video, another wonky behavior has sprouted up. I can't export audio from Play instruments properly. I can hear the initial note, but nothing trails off, so a long expressive violin whole note sounds like a little quick mouse squeak. I thought I'd just freeze indivudal tracks before exporting the whole thing to mp3, but then I discovered that fast bounce is the culprit here. I have to freeze tracks in real time, and one at a time. With a 17 minute piece that is a long job. Is there a way to tell Sonar to freeze all tracks, then set it up to run overnight?
 
And I know, I shouldn't be having this problem. "Shouldn't be" NOT EQUAL TO "am".

Resonant Serpent
According to your signature, you're using an M-Audio Delta interface in Windows 10. Did they eventually release Windows 10 drivers for the delta series? Last time I checked for a friend, there were none. If using a legacy driver, this could be a large source of your problems, and might be best to get an interface that is compatible with Windows 10.
 

Depending on you model, the last driver 6.0.8 from way back works fine in Windows 10 with Delta 44, 66 and 1010 cards, zero issues. I still have 1 machine running Windows 10 and a Delta 1010, no problems at all.

Starting with Play version 5 there are numerous issues with it not playing notes correctly (release samples not being triggered I think), especially when rendering.  There is at least one other thread about this.  Recent updates haven't really helped and EastWest hasn't exactly been responsive. 
 
The problems, at least for me, had gotten so bad I rolled back to Play 4.3.5, which doesn't have the broken disc streaming/memory usage issues.  Rollback wasn't a big deal if you haven't been using the VST3 version of Play (which is a new addition to Play 5) and aren't using the Ohmicide and SSL effects (the SSL effects do exist in 4.3.5 but require you own them, which I do, but I think they made them free in Play version 5).
 
The 4.3.5 download is still on the EastWest site (since it's the last version that has 32-bit support).
 
Going back to it solved a bunch of bad note issues with Hollywood Orchestra for me.

According to EW, the 4.3.5 version only supports 32-bit, so I'm not going to downgrade. I found some information about a caching setting that might make a difference, but I'm yet to test that. I froze some of my tracks and that seems to have cleared things up for the time being.
 
After some research, I learned that my Delta Audiophile 2496 driver is up to date.

No, it's the only version that ALSO supports 32-bit.  The installer is for both the 32 and 64 bit versions.  Starting with 5, they removed 32bit entirely.
 
And this problem:

I can't export audio from Play instruments properly. I can hear the initial note, but nothing trails off, so a long expressive violin whole note sounds like a little quick mouse squeak.

 
 Is exactly the reason why 5.x is unusable.  It doesn't correctly play releases.
 

jkoseattle
According to EW, the 4.3.5 version only supports 32-bit, so I'm not going to downgrade. I found some information about a caching setting that might make a difference, but I'm yet to test that. I froze some of my tracks and that seems to have cleared things up for the time being.
 
After some research, I learned that my Delta Audiophile 2496 driver is up to date.

 
It looks like a platinum BUG, your audio interface is not responsible.

If you have a repo that causes a crash in your project then you have "GOLD" my friend.
You can disconnect each instrument via Synth Rack by "GROUP: ALL kontakt try repo, then all session drummer try repo, etc etc " and use the repo to confirm its not a particular instrument ! < DO THIS i have many repo's i have solved like this, just make sure you disconnect all or any of the same instruments each time.
 
 
I looked at your video, what instruments are you using exactly ?
Brass, Strings, Percussion what are these Kontakt ?