I don't think so, your theory is kinda uncomplete in terms of data structure modelling. Say you want a simple Half-Life (you should know about this game, don't you ?) 3-Dimensional geometrical level to load as fast as possible, it doesn't matter how or when you want to display your level. As a first step, the main problematic is that one standard level involves more than geometric datas, that is, you have mainly the Texture's to load from file as well as Sound FX's and even Scenario's. That has much more to do with the compression you use than the amount of data you store. Then those Half-Life levels couldn't share more memory than the machine can, that means data is whether or not compressed, either loaded from files and put in cache/buffer but never let stored in their original files where the game Engine cannot manage each type of data to load on real-time if their type and compressed data don't get "normalized" or loaded previously to the real-time rendering begins.
As a matter of fact, a game-level is something you cannot "split out" if it ain't previously "swallowed", where the hazard is to get struggled with the amount of data your engine is using.