Summary of the Primary offenders causing combat to take so long:

1. Terrible AI delay. This is tied to enemies having far too many abilities/consumables compared to what they should have.

2. HP Bloat. Increasing enemy HP only serves to delay combat. Fix enemy stats to be what they should be under the rules of 5e and what your Shatter/Sleep be as effective as they're supposed to be. A GWF Fighter should be killing every goblin they hit.

3. Overabundance of Surfaces. This significantly slows down the ability of melee characters to get into combat.

Fix those three and combat gets a lot better very quickly.