Hi!, glad to read someone who have the same problem!... i posted this issue like a week ago and it seems to be a software issue in iOS 9.1 and above (still present in iOS 9.2 beta 3).
Right now the only hope we have is to wait till official 9.2 arrives and fixes the bug... the most extreme option is take a trip to the store you bought it and ask a replacement, i took the phone to an apple reseller and they said that the best option is to wait till apple fixes it, because they don't believe it could be a hardware issue given the circumstances the bug actually happens. In my iphone (iPhone 6S 64GB) at least it doesn't happen too often...
Hope it helps! you must be patient