I had a similar issue however on my Galaxy S7. I came here while doing a quick Google search (no idea why I didn't come to the forums as I am a member, lol).
I found this article and a more specific one that outlines how to reduce battery drain aka increase battery life on the S7.
For me, I noticed that the article references the use of a task killer which I did install. However, in this thread, I noticed that there is advice against using such apps. On my S7, I used the task killer with no issue. But, when my brother installed the same on his Galaxy S6, it only made his problem worse.
I would think that the different software/hardware caused the difference between both our phones re-acting differently.
Other things that I did on my brother's S6 included,
changing the GPS settings.
Changing the sync intervals for emails.
Changing the notification settings.
Uninstalled the task killer.
Reduced the brightness.
His S6 works better now. And, my S7 works great sans the task killer as well. However, works just as good with it installed.
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