I presume this scenario is a hybrid of multiple games that had issues with porting; the elevator one sounds like a reference to Portal 2's abysmal loading screens. Either way, that one had an easy solution, assuming the elevator is enclosed: Just make the elevator itself a separate level as well, and unload the previous level and load the next one while you're in it. Boom. This is also what Valve should have done, for the record, as I've been saying for years.