I'm 68 kilos and have an f12 and would say around 13-14 knots would be about as low as it will go with a big directional. I ride a 135 ply and fine 15 will just get me going and feel really good at around 24. Although Ive only been out a few times I know I can get better bottom end and top end.
The trick is dive the kite hard and go with it downwind a bit to build up some speed then just edge upwind and the kite should generate enough apparent wind to keep you going.
But whos cares about just going I want to fly baby YEEEE HHHHAAAAA
Give it ago in 20 knots and see how you go.