If your system resources are not up to par when loading a VSTi a few times another option is to load the VSTi, record your violin part, bounce said part to a wav, mute-archive and hide that MIDI track then repeat the process until you get what you want.  When my old computer couldn't handle a few cpu intensive VSTis any more and that is what I had to do until I saved my money for a new computer.  A PITA for sure but this process does work. 
 
If you are using the same violin sound be sure to either add a little chorus, slightly detune it or both.  But it is better to use a few different violin sound sources.

Hollywood Orchestra contains instruments that are already ensembles of multiple violins. It includes patches for the whole 1st Violins and 2nd Violins sections. You don't need 1 track per violin. Just pick the relevant patch, and use it with 1 MIDI track, or 2 if you need separate 1st/2nd sections.

The manual is an interesting read even though i do not own it.  It is obvious that you can have a number of separate outputs for Audio (the example the give is even SONAR) and then within any patch you can assign different midi channels to those voices for which you can add more midi tracks assigned to those midi channels.
 
Page 120 in the diamond manual for assigning audio outputs
 
Page 60'ish for assigning midi channels.

Nick Phoenix has some good tutorial videos on the EW site for HO. And you really need to read the manual for HO. It is powerful and complex. As already stated there are sectional patches included. I'm curious as to why you need 15 violin tracks unless you need to load multiple articulations?

I have a short article on how my template for HO is set up on my website. Here's a link. Maybe that will be helpful.