Hi Carl,
I read that the target PN for this class is in the 80 to 77 range. Your SC15 is already there, old PN = 78.
The PN difference between the SC17 and SC15 was 5 points in the 1980s, 78-73 = 5. At the Tradewinds Race a few weeks ago the ARC17 sailed to, demonstrated, a PN of 70.1. The major difference between the SC17 and ARC17 is square top main and self tacking jib which has a much longer jib luff. Apply this sailplan scheme to the SC15 and you might have a SC15 capable of sailing to a PN of 75. Then add spinnaker and knock it on down to 72. No new technology required.
It sounds like many people interested in this class are talking about taking an old existing platform and working on the rig and sailplan. That's fine, and it is also low cost. What will throw a big bucket of cold water on this class is for someone to build from scratch a superlight weight boat that sails away from everything else because of its weight, not because it is a better design. To get this class going and keep it alive, it must have a minimum weight that is easily attainable. It sounds to me like a rule that says you must use an existing production platform would not be out of line with most sailors objectives. To keep the cost down, keep the minimum weight up.
Good luck,
Bill