What does the bike have out of the shop? 10w?

I remember having an Aprilia Shiver with really soft forks. The shop said they could try changing it to 15w, and I must say it made a great improvement. Mind you the Shiver is a bike for fast corners and racing around town. Driving around town over tram tracks, cracks and cobblestone was hell, though.

I test rode an "old" 660z before buying the "new" 2011 ABS Tenere with shorter suspension travel. The old one felt like driving around on a cloud/waterbed so I can imagine it would benefit somewhat from 15w oil (if it has softer by default) if you want to get better road handling at least. Wouldn't put it in my ABS version, though. Shocks are much firmer.