I'm not using any kind of optimazition and it runs very well, though my laptop has nvidia gpu with support for newest opengl.
Anyway back to your problem, I assume you're using laptop with either old graphic card or with intel graphic card ? Krita is using opengl for scaling (by default) and that's your problem, intel gpus are not supporting opengl. So the only thing you have to do for krita to run smoothly is turn off opengl scaling...
So go to Settings -> Configure Krita... -> Display -> and uncheck the opengl option
Krita should run way faster after you do this