I think I remember reading an article (it may have been Turbo Play), where they were talking about how the game levels stream from the disc. That would almost imply that level graphics/maps are too large to fit into memory all at once.
It's been a while since I've played this game, but maybe someone here can chime in regarding how large/complex the levels are, and if there are many noticeable load times, during gameplay.
I wonder if any other ICOM games employed similar level streaming technology back then. I don't think this was all that common of a technique prior to the "playstation era".