I’m usually at least 2mph faster on my time trial bike than on my road bike even though my road bike is 3lbs lighter at 17lb vs 20lbs for my TT bike, riding the same routes. It’s the much better aerodynamic body position with lowered head and shoulders plus the bike frame itself is flat and skinny, and the aero wheels help too. All that aero stuff costs money no doubt but you might get lucky and find a used TT bike cheap on EBay or such.