Performance of a game with the scenery divided into several maps

I’m working on a personal remake of Haunting Ground, my main focus is to learn how to use the engine in a “Simple” project. (In my opinion, if it’s a personal Fan Remake this is the best option because you do not have many guns , there are only 2 enemies, Homunculi, luminessants and of course the pursuers that are few, so I’ll spend more time in level Desing).

But one thing that embarrasses me with this kind of project is what I think the scenarios are divided into small maps and the doors are the loadings (like the Resident Evils Classics), so in gameplay the performance of several maps being loaded instantly would be low because whenever the character crosses a door the previous map would be unloaded and the current one would be loaded, remembering that enemies and persecutors would do the same thing as if it were a single map.