I guess that depends on how fast you want to be going. If anything, 48/17 is a touch on the high side already for an around town / city bike.

At that ratio, 90 rpm is 20mph, with 115 rpm being 25.

If you're hitting those cadences easily and want to be going faster, then you can go to a bigger gear.

If you're mashing at 70 rpm and upset because you're only going 15 mph, then you should just work on increasing your cadence.