So, this behavior from Samsung phones is really not new, and it has been around since the S2! Some anecdotal evidence (oxymoron huh?): My wife used to own the Galaxy S2 when I met her, she usually complained about a draining battery which I completely understood seeing as how she was using it for videos and netflix, back before battery management was matured, but funny thing, my LG Lucky was getting more life than hers! Later down the line I purchased a Used S3, and its battery life was good, but not great. It lasts anywhere between 9 - 12 hours depending on my usage, which puts it directly at odds of what I have seen with other S3 owners! Recently, a friend of mine upgraded from his S2 to an S4, and his battery frequently dies less than half way through the day, this happens so much we purchased a rechargeable battery pack for him to carry to recharge his phone during the day. I purchased an S6, surprisingly it hasn't failed me. I am keeping my fingers crossed, because by the end of the day, I still have about 25 - 30% battery life on it, and this is after 16 hours.
So Linus, you are not alone.