How to determine size of freewheel?
the 14t, 15t, etc. is the number of teeth. You currently have a 16 tooth or 16t freewheel. More teeth and the easier to spin, but the slower it spins. Think of teeth on the rear cog as inverse to ease...lower numbers take more power to move; higher numbers take relatively less power. You want to find a good mix that allows you to make it up whatever hills you have while still not requiring a super high cadence for the flats.