One of my goals is to run 2 miles in 15 minutes. I'm about to successfully do this on a treadmill, but I'm wondering how 15 minutes on a treadmill will translate to real, outdoor running.
Treadmill is a lot easier. Better than nothing, and good for speed work or for cold weather, but in my opinion they are not the best training option. With the belt, it propels you, but you have to propel yourself outside.
A good rule of thumb to mimic the EFFORT of outdoor running is to run on the treadmill w/ an incline of 1.0 or 2.0.