Wade,
I would imagine you looked at the total width of the case. The cooler does not mount to directly to the side panel. It is on framework of the case, and raised pegs on a motherboard. The information below is from the case's website and the cooler's website...
Case: Max CPU cooler height: 162mm / 6.4 inch
NH-D15: Height (with fan) 165 mm
So.... I don't think it will fit with a fan on it.