Lollipop ROM optimization help?

I had recently flashed CM12.1 official nightly build along with run n gun lite kernel and L speed mod, the phone's running good, but on many apps, such as Facebook, the phone shows sluggish performance, is their any way I can minimize the RAM consumption?
Any recommended launchers, keyboards, mods etc? And secondly I'm also facing Play Store 504 error on my phone too.