Hi!
I ride a MTB on paved roads pr paths and while it is more work at first, you do get stronger and then it 's no big deal. It might wear the tires faster, which means buying new tires = more $, but then you could just buy a pair of slicks.
A friend has a pair of mixed tires - slicker in the middle for road, but with knobby edges to help grip off road. She likes this combo.
Either way, it's funnnnn!