It doesn't matter what size boat you say you're looking for, someone is always gonna say to go bigger. Looking for a 16' boat? Someone will say get a 17-18'. Looking for an 18'? Someone will say to go 20'. A bigger boat also means a bigger outboard, which is a big chunk of the cost.
I'm also in the market for a 14-15 footer. The dimensions of my garage say that size + trailer is what I should get. Lots of junk out there on the used market and good deals go quick. Some guys selling need to look at the prices of new boats before listing their POS. Throwing a couple of life jackets and rod holders into the deal doesn't make your boat and rusted out trailer worth the price of a new one.