As always, it depends on how you set your level up.
I don’t know how you set your world up, however:
My large world loads and unloads levels based on player location, but for more compact areas (like my Downtown area), I use PACKED LEVEL ACTORS that can be hidden or culled; very quick retrieval and although it doesn’t improve FPS/MS as much as a full unload, it still is better than being visible at all times. So, PACKED LEVEL ACTORS may be what you want, in addition to your current setup; they can act as an in-between.
You can also just make your sublevels invisible, which will save FPS/MS, but still take up space because they are loaded:
