Keep in mind that it's not just the RAM clearance issue you'll have to worry about, it's also the case you're putting it in. You can raise the fan on the NH-D15 up to get some clearance for the RAM but then you're possibly running in to issues with how much CPU cooler height your case supports. Also when you raise the fan, you're decreasing the amount of air flowing through the cooler it self, so at some point you're going to hit the point where it's just not worth the hit to the cooling.
Corsair Vengeance comes in two different models, low profile and their huge heatsink sizes. The Vengeance Low Profile should be around 32mm, which means you won't have to adjust the height of the fan. The standard Vengeance is 52.5mm, so you'll need to adjust the fan up by 21mm.
Ripjaws X comes in at 40mm, so you're going to have to raise the fan by 8mm to compensate for that.
Overall I'd say look at a difference CPU cooler for your setup. Have you looked at the Cryorig models at all?