So i've had this issue for a while now, on CC 2014 too.
Once my timeline gets relatively full and i start doing rendered previews, premier just seems to freeze up, hang and the only way to continue is to force quit then re-open the project.
It seems to work again for say another 30 minutes then does the same and i have to repeat the same process.
I've tried many things and i cannot seem to find out the sequence of events that is triggering or the cause this but it's become such an often occurrence and is a huge pain in the butt, so much so i'm considering moving to a avid workflow.
I get this commonly on what aren't hugely complex edits, a great deal of fast cuts but no effects work whatsoever and it seems to have a fit. Surely rendered preview files should help the process, not hinder it.
Mainly editing 1080p AVCHD, XAVCHD and Pro Ress'd media.
Disk speed should not be an issue, edit drive is around 350MB's read/write.
Anyone having this same insanely annoying issue and have any solutions?
Repairing disk permissions
Deleting reference files and rebuilding them
Deleting Preview files
and so on.