Getting a new laptop which will at times be used for recording vox and acoustic guitar, and will be located in the same room as the artist (me:).

• Two options: a 15.6" laptop with a cpu that maxes at 15 watts, and a 17.3" laptop that maxes at 37 watts.

Will there be a substantial difference in fan noise that could interfere with recording?

Sorry for the diversion, but why get a laptop? Why not get a desktop? You may have your reasons but if it's going to stay in that room a desktop may be a better bet...

 
Whatever makes the laptop run cooler will help with the noise. Use onboard-cpu graphics, ssd, disable all unecessary processes, etc.
 
Put your laptop behind the couch or under the bed.
 
 
 

Thanks, Alex, Paul.  The laptop purchase is for my wife, and would be convenient for me to "borrow it" to do the acoustic & vox recording. My alternative setup/scenario, is to get a KVM splitter, which will allow me to attach a 2nd keyboard, monitor and mouse, and run extender cables into the next room where I'll be recording, so I can access my primary recording PC. No noise, just a bit more complex.

Laptop fans aren't that noisy compared to a typical desktop system. Even with a PC, I record in the same room without issue.
 
If you go laptop, just make sure it has fast external connections for the audio drive.

I would be surprised if the laptop had a fan. 

John
I would be surprised if the laptop had a fan. 

I've never had one that didn't.. at least in modern CPU times.

I must say I have never noticed if one had a fan or not but I would be interested in where the heck they put it. LOL.

I bought a Dell Inspiron i7 a few month ago and it had a BIOS issue that kept the fan running at full speed.  It was LOUD!  After flashing the BIOS I couldn't hear it at all.  I returned it and got an ASUS which has a fan but I never hear it.  I use it for recording anything via a microphone since my desktop is not quiet enough.
 
 

jscomposer If you go laptop, just make sure it has fast external connections for the audio drive.

Hmmm...what do you mean, fast external connections for the audio drive? My Fast Track Ultra is a USB 2.0 device...
 

vintagevibe I use it for recording anything via a microphone since my desktop is not quiet enough.

My PC is my primary recording box and is truly a silent PC --- I love the PCs I get from the silent PC mfr. I buy from.