I would strongly suggest using Vienna Ensemble Pro with big templates.
Can a mod please, please, please chime in and tell me whether this is being worked on?
Better 2 fill in a support request form if you really want attention from Steinberg.
For what it’s worth, I have a VEP based template and also suffer from long save times. There are other forces at work.
I was having the same problem in 7.5 and managed to solve extremely slow saving, at least semi-permanently, through repairing permissions. By which I mean: closing the app and immediately repairing permissions, not going through Recovery mode. Not sure if you can do that in El Capitan now.