OP, you should check this video out. It's about what happens when planes depressurize and why you need to put your mask in first before helping others. https://youtu.be/kUfF2MTnqAw
Falling unconscious in 15 seconds is not only realistic, it's generous. Dying in 15 seconds seems more correct. Because this isn't low pressure, this is a vacuum!
Now, what makes sense in a game and what's fun to play around, that's different. I'm not saying you should make it so you die in 15 seconds lol. Only sharing this since you seemed to believe longer was realistic.