Earlier on I used a lot a 14m Torch 07. But the last 1,5 year I didn't use anything bigger than 11m.
It also depends on your quiver, the gaps between kites and your budget
ex. 13-9-7 or 11-9-7
On some light wind days a 12, 13, 14 or bigger will definitely be useful just how many days a year or sessions do you have like this? It depends on the place where you kite. HP freestyle with a 15m kite, boots or straps & nice steady breeze is definitely sweet!