As the others have said, you need to play around with your stance a bit. I have no idea what stance width/angles I started out with but, over the years, I've settled into 12/-12 on a 23.5" width. I tried +15 on the front for a while, but I felt it in the inside of my lead knee after half a day. Personally, I like a duck stance so that I can really get low without feeling like I'm tucking one knee in behind the other, but that's just me.
One thing that I would suggest is to take a measuring tape to your existing stance and write it down somewhere. Tweak one of your variables and ride for a while. See what your knee says. Just don't go all crazy and change everything in large increments all at once. You'll be chasing your stance all over the place in no time by doing that.