I downloaded the nightly from yesterday evening. The performance-improvement is noticeable, could be very well factor 3. Still not as snappy as my own schematics, but workable (medium laptop with intel I5-1135G processor, integrated graphics).
I noticed another (different) issue with the hierarchy-panel on the side.
Selecting all 32 subsheet-rectangles on subsheet “Digits” (page4, top right side) and then move that selection causes the hierarchy-panel to scroll 3 times from top to bottom.
With so much subsheets (>300) this needs much time, stopping the workflow.
The difference in reaction-time can be seen if the hierarchy-panel is switched of intermediately.
@JeffYoung : will you look at this or should I open a gitlab-issue?