Hi and thank you for your response !
So I tried with an actor blueprint and put a load level instance in the construction script as you said, but the editor crashes anytime I put it on the map… I get the error message : “Out of video memory trying to allocate a rendering ressource. Make sure your video card has the minimum required memory, try lowering the resultion and/or closing other applications that are running. Exiting…” I have an RTX 3080Ti, 32Go RAM and i7 12700KF and I am able to open and work on the level if I open it so I don’t really get it… I also tried to link a nearly empty level (a box and a dir light) but everything is lagging like hell. I think I’m gonna try to merge everything but that means I won’t be able to modify it directly in the persistant level…