My perspective is from using the polar images from the airfoils and not real experience (though I have some of that too), anyway I just thought I mention that I thought of this today and what I found on the NACA 2415 is that it has a very much optimal stalling characteristic so it just seems very difficult to find a tip airfoil that actually have a better stall capacity than this. I did find however that the NACA 2315 should be slightly better at the tip with just a little more gentle stall curve that stretches the stall point just a little further.

Then I thought that if the aim was to make the wing more similar to an aerobatic aircraft, perhaps it would be an alternative to turn things around a bit. Because if you had the symmetrical NACA 0016 at the inner section and the stall superior NACA 2315 at the tip, that seems to make a perfect match with no washout.

Any thoughts of that?