I remember once that I used a brush tip that was something like 800x800 pixels. I sized it down to something like 6 px in the brush engine. Still, when I made a stroke, it slowed down ridiculously.

So, does the original size of a brush tip affect performance? I like to be able to scale whatever brush I'm working with, but if the original scale hinders performance, it may be smartest to downscaled the graphic before importing it as a brush tip.

There are several parts to take in account for the presets performance, mainly the engine, thus any brush in the pixel engine is much faster than any one in the color smudge engine, when you get to know the main differences between the engines, then you can choose in an easier way for what to customize without ending with a terrible slow brush, you also may notice in the presets editor that the more effects active, the longer it takes to compute the strokes, and how some engines have more options than other ones, the key is to find a good compromise between effect and performance. (I would stick with the pixel engine to begin with if no other effects are needed since is a multi threaded engine )

https://docs.krita.org/en/reference_man ... gines.html?