iPhone 6S Restarting

As of earlier on today whenever I try to do something my iPhone keeps on restarting itself, I haven't changed anything and I attempted to update it but it doesnt last long enough to update. It started when it for some reason shut off at 40% and went down to 6, i charged it for 2 hours to come back to it being 6%, i wanted to see if i could backup and factory reset but it lasts about 15 seconds and then restarts, is my only option to factory reset to see if that helps it?