slick (and similar) tires will make a significant difference
the tires can / will weigh less - and will roll better (less rolling resistance)
but it still won't be a road bike (but for some that is not or barely a negative)
rode MTB with smooth tires on the roads for years during the colder/winter months ; used smooth tires in sizes from 26x1.0 back in the day to just fairly recently 26x2.15 (and many in-between)
this worked well for the shorter group rides - as long as everyone was on a similar bike ... if one person showed up with a road bike then there was some grumbling ... lol
to use these narrower tires on a mtb, do we need new wheels or can we use stock oem mtb wheels the bike comes with? thanks.