They used 10weight in mine. The springs will make the frt much stiffer. I didn't want to add to that stiffness with a heavier oil. Glad I didn't.
At 25,000 my front OEM springs were gone. For the first few thousand after the Progressives were installed I thought my teeth would jar out. Very rough at first, now I love them after about 6,000 miles.
i have always used the eigt of the loaded bike for deciding what wieght of oil to use .i am 200 lbs and my wife is less and i tried useing the 15wt and iot was too stiff i would recomend if you weight more than use loaded you might want to use the 15 if not it is always good to stick with what honda says...just my two cents..
If i remember correctly, i think that phil flack rally services installed 15/20 weight fork oil in my wing. I also replaced the rear spring to progressive as well. My wing rides smooth, no problems, no dragging.