I updated my Rogers Samsung GS6 with the new Android Marshmallow release and now have a phone that dies multiple times a day. It drains the battery down to 1% most times.
The phone also gets so hot it actually is uncomfortable to hold it.
It appears, but, i am not sure, to be that the screen itself is to blame. I.E, according to a battery checker I have, the screen is using 75% of the battery. I never saw that in the Lollipop version of Android.