Seems to me that if you put a 16" tire on a 15" rim, you run the danger of the bead letting loose the first time any side pressure is applied to it. Further, it probably wouldn't hold air anyway.
My wife's '09 LT has Metzeler ME880's on it, and she loves them. Me, too. And the rear is a 15" 180 series tire. I'd say that if one wants to put a 16" tire on the rear, then they'd have to install a 16" rim. Lots of folks use a 200-series rear tire on their 900 because it seems to look better and because it has thicker tread, it has a larger outside diameter that results in making the final gearing taller, so the engine turns lower RPM's. Makes for a more relaxed cruise at higher speeds. The downside is that one will experience slightly less crisp acceleration. Won't be quite as snappy when you roll on the throttle, but I expect that it wouldn't be very noticeable.
"Don't sweat the small stuff---it's all small stuff"
'09 650 VStrom