Same problems here. I've had my t-mobile S6 for 1 week, this is my 2nd one!! I thought I had a lemon the first time so I exchanged it for another. Coming from an S5 the battery life on this S6 has been terrible, everything else on the phone I love, but the anxiety I feel as I watch my battery drop over 10% per hour in standby is ridiculous, if I use the phone it drops 15%+ per hour. I've done a factory reset 3 times. This last time I didn't even install any apps or turn on wifi, I went through and disabled all the bloatware, voLTE, and all the other suggestions everyone claims can fix the issue. Even with no apps, no location, no sync, no wifi, no google account, it still drains 10% per hour in standby.
Not sure what else I should do, if I can't figure it out I guess I'll go back to my S5 which would last me easily from 8 am to 10pm. I'm not a heavy user at all, 1-2 hour SOT is probably all I need plus 10-12 hours standby. Never been an issue with any of my Android phones dating back to the G1.