I have both the S5 and S6 also. So far, to me, set up identically, the battery life seems to be neck and neck. I think that the S6 may be slightly better, but can not really confirm anymore (The S5 is no longer connected to a SIM, so can't make any more direct comparisons).
One thing I will point out is that network connectivity makes a huge difference. With my S5, when I was at home Wifi, and idle (i.e., light use to check emails/texts), I would lose about 1.8-2% per hour. But, at work Wifi (also Idle), I would lose 2.6-3%. Can't explain why, but clearly the difference was the different Wifi setups.
With the S6, home idle time is about the same. The work idle %loss seems a little better, but its still a little early to tell for sure. So, difference in the Wifi (or cell) network will make a difference for different users.
Another thing to note: Rogue apps. Sometimes, with my S5, I would notice a sudden spurt with the %loss. Checking Gsam, I usually found it was a particular app (several times, it was Myfitnesspal) that once I closed out in the task manager, fixed the issue. So, now we have a new device with a relatively new OS, and it wouldn't surprise me if some were experiencing issues with the occasional rogue app.
Anyway, I hope this helps.