A slowness is observed in the rescoping process when the PR have large number of participants. During the rescoping process, the majority of time is spent to load the pull request objects.  Each of these objects take a long time due to the large list of pull request participants. That list is not used during pull request rescoping, but it is loaded since later the events are dispatched that contains the full pull request object, and it needs to have its participants initialized.

There is improvement opportunity by batching participant-fetching that can speed up  applying rescopes