At your size, I am guessing your 15m is gonna be your "go to" kite in our area.
I think Dennis rode his 14m Sonic nearly every time out last season.
Most ride-able days here last season stayed under 28 knots.
Thing is, when it goes over that, it can REALLY go over that, so most riders (regardless of size) have a 12 and a 9 along with the 15. I rode a lot last year (160 pounds, rode nearly every ride-able day) and only needed less than my 11m Instinct twice.
The prior season though... man... we had a lot of big wind days.
If it were me, I think I would get a 10m or 12m, depending on the low end of the particular kite and just hop off once it went nuclear if you can't get two kites. You might be able to grab an 07 7m waroo cheap for high winds.

I bet the 9m waroo is the most common kite too, btw, but you are a pretty big guy.
Bleighty, what do you think?