So, are you people with this drain issue turning off Scanning Always Available and Smart Network on your Wifi Settings?, Also, there is an option on my onePlus One (Kit Kat) that as far as I remember it was on my S5 so it may be on S6 also, that says Avoid poor connections, does the S6 has it?, if so, can you try turning all the above settings off? Again, none of this are needed and together with VoLTE and Wifi calling are possibly causing the battery drain for some of you, that could explain why some have it and some don't it may easily e related to the combination of this settings.
I always turn all those and some more off, again, if I don't need them I always turn them off and I'm not crippling my device like some of you have mentioned, having a Smartphone don't mean that you have EVERYTHING on all the time, that's the beauty of the Toggles.
I'll know for sure on Friday when I finally get my Edge, but for now, you can do the tests to see if we can finally pinpoint the issue.