A few years back manually quitting apps might have been a prudent thing to do, maybe even up to KitKat or so. But memory management in Android gets more and more sophisticated with each version so at this point you're more or less just making your phone work harder to compensate for your attempts to micro-manage things. In other words, the Android operating system is better at maintaining itself than you are.
Try uninstalling those task manager apps, most of them are just added fluff using up system resources better left for things that should in use, and take a little time working with what's already in your Settings menu.