Good advices were given above for a true planing hull above 7/8 knots winds with +11 m2 sails. You will need to extend the upper wind range of your SUP up to that wind value to cover it all.
However, for true 5-15 knot wind range, you can also consider a Phantom 380 with a grunty 9.5 sail. You have both world of gliding and planing with only 1 setup. Much more fun than schlogging on a Formula/wide iSonic below 7/8 knots wind limits but slower than a full-on wide planing hull above 8-10 knots. The bonus is that you can skip the costly addition of a newly complete +11 m2 rigg setup.
By playing the devil's advocate, have you tried your SUP in 10-15 knots winds already? What kind of sails are you using ? How good/bad is it WRT schlogging/planing ? Most importantly, is it fun to you ?