Bruce

It's not my idea, dinghy sailors have been using them for years, I have never made one, only seen them on other boats, so I don't have one to show you.

As to size/shape 15 sq m is about 150sq ft, The best kite shape we have used is the one on our 18HT, I am really pleased with it, I would simply scale it down which would give you a hoist height of 7.1 m, which is about 23 ft 4ins.