I have the S7 as well. I just took the bug fix update this morning, about 2 hours ago. It wasn't a major software overhaul, just a couple of bug fixes to touch and something else, and a bit of stability--fairly small and quick. My battery is fine so far. It was at 80% directly after the update, it's still there, and I've been on the internet, etc. I know 2 hours isn't long, but with battery drain, it's long enough to notice if it's happening. On my S4 occasionally apps were sucking the life out the battery, dropping it 30% in 20 minutes of no use. That drain is not happening for me right now on the S7. My Android System is using only 10% of the battery right now. You can try power saving mode, but on the S7, power saving mode stops some apps from working properly, to save power.
http://www.gottabemobile.com/2016/04/12/samsung-galaxy-marshmallow-problems/ -- From this article you can link off to help pages, but if you're reading XDA, then you're likely already aware of everything in it.
Fingers crossed that if enough people complain now, a bug fix to your problem will arrive sooner than later.
And you can factory reset -- just Google that, lots of help around to walk you through it if you go that route.
I ll try my best to list the steps. Flashing official firmware doesn't trip knox.
1- download odin and unzip file
2- Download official firmware and Unzip file. theres 4 or 5 files AP, BL,CP, CSC and HOME
3- Open odin and load AP file from the firmware you downloaded
4- Load BL in the BL tab.
5-Shut down phone, then hold power button, volume down and home button together. download mode will appear. press up to continue.
6- Connect your phone to the computer via USB, odin should detect. Press Start.
Your phone should restart and erase everything.
Note: By flashing AP and BL only, your phone will not detect the new update PD3, which means if telus pushes an update in the future your phone wont detect it. The solution to this is you have to flash the same firmware but this time with the CSC and CP.
The first time I flashed the 4 files, soon after the phone booted I got a message that theres new update that I couldn't swipe away, that's why I only recommend flashing AP and BL for now.
You're welcome haha. You don't need to root or anything even though that page says otherwise. Your warranty isn't going to be effected. Knox is only tripped when you root the device and install a custom rom and a kernel. Since this is an official firmware theres no worries