There was a thread a few months ago discussing the speed of the Fill Tool:
From that some improvements were made in the 5.3 branch, including to only update the part of image that was changed so the speed wouldn’t be dependent on image size:
There was a thread a few months ago discussing the speed of the Fill Tool:
From that some improvements were made in the 5.3 branch, including to only update the part of image that was changed so the speed wouldn’t be dependent on image size: