My Macbook Pro (15in, mid-2015) has been decidedly laggy and choppy when doing things like scrolling, or resizing windows, or even just dragging windows about.
As usual I tried all kinds of things, including a full reinstallation of OS X/macOS.
It turned out the fix is blissfully simple: Turn off automatic brightness adjustment. You’ll find this option in the Displays section of System Preferences (select the Display tab).
This will mean you’ll now have to manually adjust screen brightness to maximize the battery life if you’ve a portable Mac, but it also means you’ll avoid any unwanted gamma tweaks that Apple has decided are OK for the sake of battery life.