Take a small bottle, fill it with water and add some sugar in it. Then if they say that you need to run fully packaged, with you rifle and your backpack, just unload the rifle, and get rid of the weights inside the backpack, and add a pillow from the barracks.
Trust me, it works. And before someone flames me, calling me a cheater, go and run yourself for a mile and a half.
And that does absolutely no good in the long run. Are you going to fill your pack with pillows and unload your weapon when you go into combat? Best to train for the real thing. And yes I do run myself over a mile and a half at least three times a week.
1.5 miles in 9 minuets is tough. You'll have to maintain a 6 minute/mile pace for the whole time. (If my math is right) I believe that is running at 10 MPH, which is not exactly a cake walk. If you put your mind to it though and train like you mean it then you should be alright. Best advice for joining any branch of the military, listen to the instructors. They may seem like they are blowing smoke out their asses, but 90% of the time there is always a reason for everything they do and say. Good luck regardless though, hope it works out well for you.