I know of it turning in quicker, I'm more intrigued to find out why people are saying "you have to have the 15mm"?
You can have them anywhere you really want to surely? Providing both sides are equal and it's not obstructing anything else, it's then down to personal choice and preferences which you only get with trial and error, what suits one rider won't maybe suit another?
totally agree whats good for 1 maybe awfull for amother all anyone can really do is take onboard what all say and work out a starting point and experiment with settings taking notes as to what does what and how comfy indvidual feels happy with, theres alot of difference betwenn a soft comfy ride to a firm harsh ride
from experience i find if you start soft and firm things up gradually you`ll get to a point that suites you