That's a great deal all day. I haven't had the 15" version but did own the 14" version awhile back, sold them to another forum member. They sounded great, just a bit drier than the New Orleans hats I had at the same time. I am sure you're going to love them. The "C" at the end of the model number means they are going to be the middle weight class (not the thinnest or thickest version) and should be very versatile.
The C denotes “Crisp,” which is Bosphorus’ middle-range weight. If it had a D in the model number (K15HD instead of K15HC), that would indicate “Dark” — i.e. the thinnest weight range for Bosphorus hats.
It’s a little confusing, but the “Dark” has nothing to do with sound (nor does B for “Bright”). It’s just a weight designation, so there’s no such thing as “crisp dark.” You got the 15” Turk Crisp hats. From my experience, though, they should be plenty thin.