Hi. New here.

I just started riding recently because I want to do a sprint triathlon later this summer. The bike part is 12 miles, hardtop, some hills. Right now I'm riding a mountain bike I got from Walmart and it takes me about 40 minutes to do 6 miles on similar terrain.

What I'm wondering is about how much of a difference I should see if I went to a road bike. (Basically I would have to try to find something from a yard sale.)

Would the difference be neglible over that distance or should it be X% easier to ride?