Out of curiosity, what kind of Storage / CPU cycles do you have dedicated to your PBS ?
Ours runs on 2x Intel M.2's in zfsRaid1 and 8x 14 TB WD in zfsRaidZ1 and backs up about 20 TB of VM Data. Prune and GC does not take longer than 4 hours ( that is the Window we have allotted for Prune, GC...