Sorry if it's been mentioned already.....
It's most likely because you have everything on a single HD. Have you tried loading everything into RAM? When you load an instrument in PLAY, go to the dropdown options menu and
deselect "Stream From Disk". This will load the patch directly into RAM, and will do so when you open the project from then on. It takes a little longer to load initially, but they won't be steaming from the HD. Works like a charm!