I have isolated this couple of objects from .blend file from the report above, and saved from 2.79 to compare:
http://pasteall.org/blend/index.php?id=52153
Subsurf modifier in 2.8 with Quality=1 makes Undo almost as fast as 2.79. With Quality=10 after making some change in scene and then Undo, it takes about 10 seconds on my machine.
It is a well known problem that the new Subsurf modifier with OpenSubdiv needs optimizations.