Forgot to purge keg for natural carbing

I just realized I forgot to purge the headspace in my keg after racking my stout into it and hitting it with 15lbs of pressure (and 1/2 the normal amount of priming sugar). The CO2 tank is already secured back in the kegerator and is kind of a pain to unhook and remove (the mini fridge is very tight, I have to take a leave everything out of it while using the CO2 elsewhere).

So its been 5 days with some regular air in there, what can I do?

Would it work to just release some pressure (hoping the O2 is at the top?) or should I dig out the CO2 tank and purge it? By now the yeast should have started making some of their own CO2.

It'll be ok- I wouldn't worry too much about it. I mean, there's a little air in the headspace of bottles, too, and it doesn't oxidize the beer. You "topped up" with co2 so the beer will be fine.

CO2 is heavier than air. Your still fermenting (Carbonating) beer is creating a nice cozy CO2 blanket on top of the beer. You'll be fine.

That is all good to hear, now I've only got a couple weeks to kick one of my current kegs to make space. Shouldn't be hard as its been feeling pretty light (wish i had a "fuel" gauge for the keg).