The 15 will start working at around 13-15, but if you want a real lightwind kite, then you might want my 21M nemesis. That is a BIG kite and I am guessing the extreme low end is around 8-10mph in flat water.

I'm selling that one for $150, kite only (no bar). It's in excellent condition also.

I was planning on selling it on ebay for around $200 but I will sell it for $150 to a local rider.

BTW, a good quiver starting with your 12 (of c kites) would be 8, 12, 16, 21.