What's keeping you from going faster?

If you are spinning out in the highest gear ratio ( which I doubt) then you need a higher gearing .

Otherwise it's pretty much the motor. Need to do some rides that aren't commuting in urban stop and go conditions. Find some routes where you can do a couple hours of easy riding with few stops. Do a few high effort sprints and climbs during the ride. At least one such ride per week if not two.

After a while your speed for anything will improve. However urban riding in stop a go is going to always average out slow.

And work on a good range of cadence too. A 60 - 75 rpm range will mean you'll have to have lots of muscle. 60 - 120 rpm range will let you go faster with less muscle.