Spot on ^ @s15
Apps like Clean Master and Battery Saver are absolute BS. They don't work, at all. They do more harm than good. They may free up RAM, but that kills some important processes and background apps, so when WhatsApp takes a little longer than usual to open, it's because Clean Master killed it to free RAM. Same for your homescreen, if it stutters or lags a bit, its because Clean Master keeps free-ing up RAM.
IMO, the only app that should be used to improve performance is the built-in Smart Manager app on S6, S6 Edge and new Samsung devices. It works great and S6 doesn't lag at all.
Makes a big improvement on my Note Edge too.
Don't ever install, apps that say they can do the following
-Make your phone faster
-Improve battery life
-Kill background apps
-Memory Booster
-Clean Master
They're all BS. The reason they have hundreds of thousands of downloads, is because people fall for the stuff they say and download them thinking it's making the phone faster.
If your phone is slow, there could be 2 reasons:
You have one of the apps mentioned above installed.
Your phone sucks and/or is old.
Sent from my SM-N915FY