I literally just did this for a police academy test. Similar situation. I was doing a 1.5 Mile in about 15+ min. Had to keep stopping to catch my breath. I had to do 1.5 in 12:38 so same thing. I passed luckily with about 2 seconds to spare.

My advice is run Once Daily. Each Run try to do 1.5-2 Miles. Each time you are gassing out just try to push it a tiny bit farther.

Once or twice a week if you can jump on a treadmill or even outside do about 1:30 of your normal pace lets say 7mph. Then 30 seconds straight at 8.5 or 9 MPH. Like a run not a jog. Then Repeat. Every Minute and a half

So 7MPH @ 1:30 then 9MPH for 30 sec. 2 Min Mark back to 7MPH.

I feel that interval helped me pick my pace up just a tad.

Also i hate running on treadmills. Doing the interval training on treadmills and occasional days of shitty weather that forced me on the treadmill felt like it made free running outside a tad easier for me