My laptop keeps shutting off ?

Update your bios if the problem persist. Or you can start system from safemode, see if it still shut off by itself. I maybe a registry problem. If the problem continues, you can format your hardrive, and install your windows again. Make sure you backup everything before you do that though. Good luck!

You mean eaxact 15 mins ,if so check your settings as Mr.Andrew said.Else it may be due to overheating you can use a laptop cooler,else may be due to some malicious program.