1 inch equal 2.54 cm. They are looking for a waist size of 37.007 inches.
At 6'5" and weighing in at 18 stone (or 252 pounds) your BMI is 29.9
Two measurements that are taken into consideration of determining obesity is the BMI and waist size.
A BMI of over 30 is an indicator of obesity and if coupled with a waist size of 40 inches would be a high risk for associated diseases.
Do yourself a favour and lose the extra weight. Don't make excuses that you are a big boned lad. Lose the fat. Make sure you do it safely by eating sensibly and healthy. You'll find your speed for your 1.5 mile will come too if you are not lugging an extra 20 pounds around.