Hey. When you’re working in the editor, the level is usually cached, so open level looks pretty quick, but in the packaged game, this isn’t the case.
Have you tried ( hear me out ), level streaming? You can do ‘old school’ levels like you have ( ie, separate maps ), with level streaming also 
Check out this tuut:
I know he's talking about menus and stuff, but if you take a look, you'll see each of them is a map / level.I think it does, but only after you’ve played it at least once…
I’m working on a game where the main character can die a lot and I am using the Open Level method in blueprint when he dies.
In the selected viewport it takes around 3 seconds for the Open Level to run successfully (this is perfect), whereas in the packaged game it takes 10 seconds for the Open Level to run.
For this kind of game 10 seconds is not acceptable and I don’t know why there is such a difference in time. I’ve even been tweaking the rendering settings and I haven’t see the 10 seconds load time decrease at all. Does anyone have any other suggestions?
My alternate solution is to re-spawn the main character at the checkpoint without using the Open Level method but I will also need to re-spawn enemies, bosses, and doors back to their original settings which is extremely tedious.
It’s weird that the packaged game doesn’t cache the level also. I think level streaming might be better than my alternative solution so I will investigate this.
I tried dying 5 time in the packaged game and it always takes 10 seconds.
Ok, then it’s streaming time 
The level streaming started to confuse me so I decided to use my own custom method to manually re-spawn the main pawn and other enemies and I get less than 1 second load time. Anyways the level streaming is another solution to this problem so I’ll mark it as the answer.
Cheers