1.5 miles in under 13 mins? That's a new one on me, it used to be 14. When I was training for the PARAS you had be able to run 1.5 miles in under 9:18 AFTER doing a 3.5 mile warm up run. Now thats hard going lol

Best advice I can give to you, is eat well, lots of carbs, brown bread, pasta, potatoes etc and bananas, get 8 hours sleep a night and for fitness, put your running shoes on and run! But in different ways for example;

Monday - 3 miles run
Tuesday - 2 mile run
Wednesday - Day Off
Thursday - Find a hill, run up it, walk down and repeat untill you spew.
Friday 1.5 mile run

The better you get at the longer runs, such as the 3 miles, the easier you'll find the 1.5 mile run. The first 20 minutes of your run is the hardest (hense the 3.5 mile warm up for the Para run, you'd be supprised when your through that enitial barrier just how hard you can push yourself), after that you just plod along. If your only doing 1.1 miles in 10 mins odd, your not even half way through the hardest bit, just keep running!