RE: Freeride board for 86 kg 6'
190 will be way to big and 160 seems kind of big too. 15 knots is not much wind though, so you should not go too small. But from the sound of it you have the technique wired for going for a slightly more "advanced" board, maybe something like an S-typ 126? In the beginning you may find if a bit technical and especially getting planing early can be more difficult, but since you're lerning quickly I think its better to go for a board that will a bit challenging.
My own light wind for fun setup is Flare 99 and a Hot Sails Maui superfreak 7.0 (the most remarkable sail I've used - light as a 5.5 wave sail). With this I plane really early and have the feel of being on small gear and still only a knot or two slower then I am on my iSonic101 and more speed oriented freeride sail in light wind. I'm 68kg though, so you need to go bigger.
Maybe Roger can chime in too. He has more experience with this types of board recomendations.