For me on my Windows machine, 16GB was not enough. I used 32 and then got a new (also) Windows machine with 64 GB ram (upgradeable up to 128 GB). 64 seems just fine. (I think one of David’s tricks (and a great insight I am following more) is to use physically modeled sounds instead of heavy sample-based sounds whenever he can. So, for example, he uses a lot of SWAM modeled instruments, Pianoteq pianos, as well as (I think) Arturia V Collection, etc. So, I think he avoids heave sample-based instruments like Session Horns Pro).
As I understand it, when Ram is insufficient the machine tries to deal with it in a way that uses more CPU.
Kontakt ram purging can be very helpful.
If you use the same “sound” in many of your Session Horns Pro instances, you could try putting that plugin in the Global Rackspace so you only use one instance of it (with that particular sound). Then in your local rackspaces, you can set up a MIDI IN block and use OSC. You should be able to add other plugins or use different splits, etc. as much as you want.
So, maybe try that. I spent a half day moving a bunch of Session Horns (not pro) instances (and a violin plugin I use a lot) from individual rackspaces to the Global Rackspace and I think it helped.
Here is the thread where I discuss it:
[Caveat, David is one of the developers of GP. There are other people on the forum who really know a lot. I consider myself around mid-range in knowledge, depending upon the issue (e.g., I am a scripting ignoramus.) So, they (including Paul) know more than me.
Jeff