I didn't ask how much time it takes Emacs to process the inputs. I
asked how much time did it take you to generate them by moving your
finger on the touchpad. I very much doubt the answer to that is 15
sec.

Yes I was talking about me inputting scrolling events for about ~15 secs. I've rewatched the video and I'm continuously swiping over touchpad for about ~10 seconds, and Emacs updates position ~5 seconds after I stopped.

> There I was talking about progressive speed turned on, as it builds up
> almost instantly with my touchpad producing 30 inputs per swipe.

Sorry, I don't understand: what builds up?

Scrolling speed. With progressive speed turned on it is impossible to use touchpad because after single swipe the speed builds up so much resulting in point immediately jumping to beginning/end of buffer.