I have a cricket s6, and 5.0.2
I try to keep open apps to a minimum, and I use the 'power saving' thing on the Blue panel when you swipe down from the top. Screen about 30% brightness. Not tooo bad. But I'm not on my phone all day, either.
Re: Battery Life
I've been using the power saver mode, the regular one, not the extreme, and I definitely see the difference. And honestly, I don't see a change in my phones performance.