Any project over like 15 mins crashes. Any ideas??

James,

how do you expect a question like that to be answered? Can you please provide further details which include:

Computer spec
File formats and standards used
how the project is made up
Are you rendering/ exporting or just playing a clip
Do you have any programs running in the backgound
What version of premiere are you using
.....

Please answer these to get a meaningfull answer.

Thanks,