The ends of the snare wire actually bend away from the head when the strainer is on, like a frown shape, so that the wires are pushed against the reso head. I don't know if or how an extra 1/2 inch on each side would affect that. Could be nothing, could be drastic. That didn't help at all.
I have often wondered how shorter than required snare wires would affect the overall performance of a snare. I'm sorry but I'm no help either, but I am sure someone will come along an enlighten us all.
The 14" can't be your only snare. Don't you have a set you can cannibalize from another drum to try out? Report your findings back here and we'll all be a little bit wiser as a result of your experiment.
If it sounds bad then just get yourself these add on a snare head or a pair of sticks and save a few bucks on shipping.