My Nexus 5x recently became so slow that I decided to look online for a quick way to make things a little bit faster. I found a quick fix that seems to do the trick up to now.
Go to Settings / System
Go to Developer options, and switch OpenGL Renderer to from OpenGL(Default) to OpenGL(Skia)
Reboot your phone
It made most lags and slowdowns go away at once. Good deal!