First off: ditch the fucking treadmill and hit the road. Use mapmyrun.com to plot a 1.5 mile course over level, preferably grassy ground, then get out and run it as fast as you can. No stopping, no walking. Now - what hurts the most? If you feel like your lungs are on fire and your heart is ready to pop, you need to start working on sprints. If your legs have turned to stone and your stride decreased at all, it's time for some long, slow distance running. As a noob both of these may be the case, but try to figure out which one slowed you down more: lack of wind or lack of leg endurance. Honing in on your greatest weakness and training to reduce it will ensure the fastest rate of improvement.