From an old elite coach.
Start at 8 Klms per hour treadmill speed for 900 metres. Each treadmill run (Min 2 per week) increase .5 of a kilometre/hour in speed and 50 metres in distance.
8 weeks you will be running around 1600 metres (1 mile) at 15 kilometres per hour or a 6 min 30 sec mile.
You trick the body with very small increases in speed and distance.
Good luck with it