The gameplay loop needed some more work, specially since the enemies sometimes take almost a minute to spawn again, which means there is a lot of downtime. The slam attack seems pointless because there was never a whole lot of enemies that needed to be eliminated instantly.
Packing the game with motion blur is never a good idea, so remember to disable it in Project Settings next time if you don't implement an option for settings, specially since it can give motion sickness to a lot of people.
The game was way to heavy for how simple it is, you probably left content packs inside the project which were not being used, making the game bigger than it needed to be. Don't worry, I also figure this out the hard way.
Overall, it has a solid foundation, but needs more work. Well done!