I got to the part with the crowbar and the beretta (with the container that you can drop). I suspect it may have to do with the amount of decals, and/or the amount of ai brains operating at that moment.
My device is a Dell Latitude 3420.
11th Gen Intel(R) Core(TM) i3-1125G4 @ 2.00GHz 1.19 GHz
8gbs of ram
It's no monster, not by a looong shot, but it's not terrible either.
Edit: It sounds drastic, but you may want to consider remaking the game from scratch in a different engine. It's a herculean task, but with the still relatively tame situations causing this amount of lag, it's like you're building on quicksand; not good.
Still, i remain hopeful, and wish you the best of luck with this honest to god fucking awesome game.