So I did what Braineack said. I went and tuned the PID, like a man. Actually I did what aidandj said as well.
I turned up I to 200 and left P and D at 0. It behaved completely differently, no oscillation. It just shot staight to overboost. Long story short I was pretty excited cuz this was the first time I actually saw it do something different. I started lowering I and eventully settled on 20. Anything more then 35 would make it go straight to overboost while anything lower then 10 would oscillate like crazy. With PID or 0/20/0 it would it would now sort of get to the desired 15psi and sort of hold it. Progress.
From there I started increasing P. I found that anything below 8 did nothing and anything above 15 made it oscillate to hell and back, much like it was doing at previously. I settled on 11 because it seemed to keep overshoot under 2 psi.
Frankly I have no idea what D does. I played with it a bit and left it at 15. It seemed to be better but honestly I think its all in my head. Please explain what I should be looking at.
At the end of the day Im left with this:
The target is 15psi and I hit it initially and then taper off. The boost duty has room to help that out significantly. Which gain will help with this?
What was screwing me up was two things. This is my first time tuning a PID and I have no idea what to expect. Every guide has always focused on P first. Without and I, my setup oscillates no matter what the P. The second thing is that from what I have seen, I was expecting much higher gain values, nothing this low.
Either way, Im feeling pretty confident about this whole closed loop thing and think I can get it pretty damn close before my dyno run on thursday.