While I like the health status site, it is very optimistic when it comes to calculating calories burned. A lot of those sites are.

Estimate about 500 calories per hour or about 30-35 calories per mile and you'll likely have a more accurate count.

15 mph for 51 minutes would put you at either 425 calories (using 500 calories per hour), or 382.5 to 446.25 (using the 30-35 calories per mile).