Yeah, the loading can be a little hard for some people especially when you're loading in for the first time due to a bug with UE4 it's honestly an issue with the engine and there's not much anyone can do about it. It's a 50/50 that it will happen so some people have this issue and some don't. I recommend that when you get to the main menu set everything to the lowest options in the settings and when you load into the game level then you can set it back after it stops lagging. If you can't even get to the main menu for some reason then you should try this article: How to fix performance guide for Marintruder
We are trying to do something about this bug however it's hard since it's an engine problem, hopefully, it will get fixed in the next engine update. Thanks for reaching out about it. I hope I helped : )
EDIT: One person who played the game had a similar issue and his game was lagging while loading for the first time and what he said helped him was minimalizing and opening the screen back to Marintruder while it was loading.