I see your 3.5" and raise you a 1/2 inch. My cruiser goes through anything.

More seriously, I would think your bike is better suited for off-road than pavement. The big tires are going to be slow as molasses on the road.
You could probably ride more miles faster on a lighter bike with smaller tires.

But I wouldn't worry about getting a different bike, as long as you're enjoying this one and you're not frustrated with the mileage or slowness. Then just get a second bike. Remember the ideal number of bikes is n+1.