Wow, that's a lot of work, location is just huge.
There is a few issues, though. To prevent the character to stuck to the walls, you can add a physical material and set a bounce to some small value. It takes a few minutes, but helps drastically. Also, would be great to have some sound indication, when the oxygen level is low. Did two times before figuring it out) And at least some objective system to know, what to do)