Sound palette is good. This is much more drone than ambient (IMO). I like how the wave moves and evolves. Not sure I would enjoy 15 minutes of this without drugs though. Listening on Yamaha HS8s. Mix sounds good for the most part but round 8:00 to 9:00 it needs some 3K to 7K EQ management (too harsh). Also needs some midrange compression or notch around the end of the piece.
Cool man sounds like game background music
I think you could have made it better if you used a little bit more fx samples like plucked or rain drops with alot of reverb and also i think a piano could have fit really great over there