Unless your rims are unusually wide, you should be able to mount tires narrower than what came on your bike. You are locked into 26" but not 2.1".
I would guess that any number of street/minimal tread 1.5" tires would fit your rims and make your bike zippier on the road.
Any bike shops you would trust to give you advice on what tires would fit your wheels?

If you post what bike/wheels you are riding perhaps someone could give some feedback about your options.