From the responses so far, it sounds like the best thing to do is try and go to a show.
Going to a show, even some of the smaller regional shows, is probably the best bang for the buck. If you can find something that appeals to you at the show, then you have a good place to start.
If your budget is $15K for speakers, though, after going to a show, I might allocate some of that to visiting some reputable dealers whom have demonstrated care in setting up their showrooms, even if it means buying a plane ticket if nothing local is promising.
In a sense, you have it harder than someone just starting out since you already have two dialed-in, synergistic systems. Do you look at your source and amps and then research compatible speakers, or do you find something in the chain you can replace to get even more performance from your speakers?