Changing semi slicks to slicks tires on MTB

[slawek371]

At first my MTB was equipped with Schwalbe Smart Sam 26 x 2.1 offroad tires, these felt quite slow and loud at asphalt, as i mostly ride on hard surfaces these were changed to semi slicks Schwalbe Hurricane 26 x 2.0 (i run them at about 45 psi) . It seemed to be a good idea as it rolled much faster and quieter on hard surfaces. Now i'm thinking about going in this direction and want to try some a bit narrower normal slicks.

I'm from Poland and live in a place where roads are very different, for simple at first i go through hard pack road in the forest with a lot of holes, next on paved rough road in the city, then i go through village on plain asphalt. There are somethimes gravel roads but the most of them are hard pack roads.

I would like to try some narrower slicks like 26 x 1.6 or 1.5 but i'm afraid that these can have too little shock absorbtion on rough terrain. i don't worry about front tire as i have suspensin fork there but rear tire i would run at a bit lower pressure to absorb some bumps.

My question is if narrower slick tires like 1.5 on hard roads would have noticably lower rolling resistance than my 2.0 semi slicks ?
Would it still be possible to make some light offroad ride to go through the forest.
As i know wider slick tire at the same pressure will have lower rolling resistance than narrow due to smaller contact patch so if i pump them at lower pressure to absorb shocks would it still roll faster than my wider semi slicks ?