You can use a gear calculator (such as Sheldon Brown's) to give you an idea of how fast a bike is designed to go under optimal conditions, but then it will up to you to reach those limits- a feat I never did achieve

I plugged the specs of the Xootr Swift (had to use a Shimano 11-32 cassette instead of the SRAM, but the cog range matches) and with an RPM of 80 on the 52x11, you'd be moving at 20.7 mph. Same combo @60 RPM translates into 15.6 mph.

Oh, just remembered that I chose 20.1.25 tires in the gear calculator since it lacked the 20x1.5's of the Swift specs and figured better to go down in size for an estimate instead of up one size that may not fit due to clearances.