I got the 15mm... if you calculate 3 degrees, that should be around an 8% improvement as I think this bike has ~ 38-39 degree lean angle (just comparing to my previous Harley which had a 39-40 degree angle). That might just be enough for me, and I have a 30" inseam and like the low seat height.
Interesting about moving upper body vs lower body - I'm the opposite. I prefer getting my butt off the seat, but keeping my head and upper body a little more centered as I feel it looks much less "racy" to LEOs and other traffic approaching from the other direction. This is just based on what I see when a bike is approaching me - I can easily see what their upper body is doing, but less on their lower body position.
Lateral G Junkie