The d15 has major clearance issues with anything but low profile ram in slots 0/1. The heatsink itself doesn't have the issue, it'll clear tall ram, but the heatsink is 160mm tall, now add a 140/150mm fan to that and you end up with @165mm leaving you 15-25mm for ram clearance. Even cheating the fan up 5mm only leaves 20-30mm in the first 2x ram slots. The NH-D14 uses a 120mm Fan on the leading edge, vrs a NH-D15 140mm fan. The performance is almost identical except for ultra high TDP, where the NH-D15 has a decent advantage.
If you plan on pushing an OC that high on skylake where you'd be skirting voltage limits of the cpu, as SR-71 suggested, I'd be looking at either the Cryorig R1, which has similar performance to the D15, or liquid cooling. The Dark Rock Pro is closer to the D14 in ability