Emerson, yes the JW Audio Cryo Nova is described as AWG 12, consisting of two solid core conductors twisted together. A 15 foot length of that cable is reasonable in terms of resistance and inductance, relative to the impedance characteristics of your speakers. And I would feel safe in assuming that the capacitance of the cable would be no problem for any reasonably designed amplifier.
Given that, IMO all that can be said with certainty is that whatever sonic effects the cables may have will be greater than if the length were shorter, essentially in proportion to the length difference. Beyond that it comes down to speculation. My speculation is that compared to say a 6 foot length of the same cable, the differences are not likely to be great enough to warrant concern.
Best,
-- Al