Not sure what prices are like by you, but both those guns are overpriced. Is the 28 Pinned & Recessed? By 1983 the 28-3s were being sold, and they are not, which brings downs the value. Is it a 6" or 4" barrel? 4" guns usually bring more money.
Assuming it is a ANIB 28-3 with a 4" barrel, top price would be $600 for a collector, but collectors want pinned and recessed guns and this one is not.
Is the Classic Model 15 a brand new gun of recent manufacture? If yes, listen to the earlier posts and find a good used one for $400-$450. The older, the better.