Agreed, Del. I had to hop on my daughter's bratty pony the other day and could squeeze my backside into her 15" english long enough to provide a correction, but no way would I use that saddle for myself. I use a 17" english, am 5'3" and 165ish.
The reason you shouldn't cram yourself into a too-small saddle, even if it's all you have, is because it CAN be bad for your horse. It creates pressure points on their back, from distributing the weight over a too small area, and can definitely cause damage from bruising to worse. You would be better to ride bareback than ride in a too-small saddle. That's not rude, that's fact.
"Keep a leg on each side and your mind in the middle"