Honestly, no. I commute on two bikes. One bike is a ~16lbs full carbon race bike. The other is a full suspension mountain bike with giant (2.35") knobby tires. The mountain bike is about 20% slower. And you can't get a bigger disparity is bikes than that.
You're not going to happy on a road bike. The riding position is going to be totally different, your spider flex seat will be miserable. Suspension forks don't actually cause you to lose much energy unless you're pedalling out of the saddle. Look at how much your fork actually moves when you're cruising along, I doubt its doing anything.
Cycling is a very strange sport in terms of what "in shape" means. Bigger individuals can ride very quickly on the flats since they can produce a lot of power. I'm a reasonably strong recreational rider on a road bike. The main people passing me on the flats are typically 30 lbs heavier.
Get a flat bar road bike with disc brakes. You'll have tons of tire clearance for good commuting tires, no fork to worry about and you'll be fine in your current position. Invest in quality tires to improve road feel and reduce drag.