Whenever I have a Sonar session with several instances of Play installed with a variety of Hollywood Strings samples, saving does take awhile. And opening such projects takes a LOT of time. I'm sure it has something to do with the number of samples in a given project, because the more samples, the longer loading and saving take.
I must say, however, that any past performance glitches have been totally solved by placing the HS library on an SSD. EastWest is very open about the fact that their test system has SSD's, and they recommend that you go SSD to get maximum performance. After experiencing for myself the difference an SSD can make, I think SSD's should be a system requirement, not a recommendation.
Having one may not solve everyone's problems, but for me at least, investing in an SSD has taken me from being apprehensive to use Hollywood Strings with Sonar...to utilizing it at a level I never thought possible.