According to the data here http://jpowell.tripod.com/saab-wheels/ the 15-spokers win by a nose -- 18 lbs. each vs. the aero ~19 lbs. each. (around 5% less). With the weight of the tire, lugs and other unsprung weight (hubs, etc.) the difference would probably under 2% or so. Not enough to make a difference either way.
Because the mass is nearly equivalent and the weight of the wheel is largely in the rim and at the center, I have assumed that there is little difference in moment -- probably safe.
On the other hand, the wheels that fit the older c900's have a couple of lighter wheels that may be a little better in practice -- the Incas and the Shelbys both weigh only 15 lbs.