According to g-skill, the aegis height is 31.2mm. What they don't say is if this is height from mobo or just height of the ram. But considering how tall a slot is adding into the fact that the ram sits inside the slot, even if you need to bump the fan upwards a few mm, it shouldn't be an issue.
The 750D has a maximum cooler height of 170mm. The NH-D15 is 165mm. It'll fit, with @5mm to spare for bumping up the fan.
Do t see why it won't work.