One of my bike is a hardtail mtb much like yours. I've so far switched out the knobbies for 1.5" Kenda Kwests. They make a world of difference for paved road riding. I've also swapped the 42t crankset for a 48t crankset from my wife's bike. She'll never need use that.
The result is a comfortable hybrid. I kept the front suspension because part of my commute entails unpaved MUPs. It helps absorb road undulations.
In terms of speed, while my other roadbike will be faster on flats, but on my 15km commute, the times are negligible. Where my road bike rocks on the paved flats and climbs, the hardtail mtb is faster on the unpaved section. Also I find the hardtail more comfortable overall.
Therefore my suggestion is that get skinnier tires and leave the front suspension alone.