I would suggest going for 20" tires initially. Like Bendembroski said, there is a wider range of 20" tires. It will make some (though not much) difference in the ride as well. 15 miles is a long enough commute.

I'm going to go ahead and outrightly name a few 20" folders that you can consider:
Columba 20" 7-speed
Schwill Loop 7-speed
Xootr Swift

Since you say you're new to folders and if you don't feel particularly brave, I suggest going with a known and reputed maker like Dahon. The Eco C6, the Boardwalk and the Mariner are all excellent 20 inchers that come with the trustworthiness of a big brand.

If you're set on a 16-inch folder, however, try the Strida. It is ideal for short urban commuting and is virtually maintenance-free. The design may take a little getting used to, there really isn't a better 16-incher for the city IMO.