Welcome to the DIS ISLES24!!
The train stops in Frontierland, Mickey's Toontown Fair, and Main Street. It arrives in each station every 4 to 10 minutes according to the Official Guide.
I think it would be faster to walk to the back of the park than taking the train if you all healthy walkers. But it is fun trip to take just for the heck of it.
Also, if you are in the back of the park and want out fast while a parade is going, I think the train would be better.
Happy planning!!