48/15 is really high gearing... well suited for use on a track, but not on a commute. Try getting a 17 or 18 tooth cog.
Most folks are comfortable with 70-75 gear inches for off-track riding. You can use
Sheldon Brown's Gear Calculator to get an idea of the gear ratios various combinations will give you.
And don't listen to the naysayers... riding fixed gear is fun, it's a good workout, and replacement parts are cheap.