Well 10mph is 9 minutes for 1.5, so 18 seconds to play with. But on the day it might be up a gentle slope (I bet it is), and everybody will be psyched up like you wouldn't believe. Most will probably go totally nuts in the first 400m and spend the rest of the effort trying to compose themselves.
I've always thought hanging on to somebody better, or trying to reel them in, results in much better times. There will be people on the day well under 8 minutes - I'm no runner but I've broken 8. So if you know someone quick go running with them and try to hang on, or if you know a route where "real runners" train go when it's busy and try to latch on to someone significantly better. Horrible, but productive.
Just to second what others have said, a tredmill gives you a false result. Not sure why but IT IS a LOT harder running out on the road. For one thing a treadmill dosent teach you how to pace yourself or find that special area just outside your comfort zone where youre not burning out but your not taking it easy. The best use of a treadmill is to watch the girls from the business park do there runs just after work . But as far as REAL running goes, I'd say they're worthless.
A treadmill gives unrealistic results because the belt itself is powered. Your legs therefore are pushed back on it, all your muscles need to do is bring your legs back to the front. A treadmill is great for cardio work, but the only way to increase your running speed and endurance is to get out and run for real, ideally up and down lots of hills.
This might sound daft, but dogs can really overheat at a constant fast pace - they can't sweat and they panic at the thought of being left behind, so they won't give up. At 6 minute mile pace on a hot day you can kill some dogs - leggy Weimarner probably ok, black lab, probably not.