For anyone who want build dual xeon machine with massive air coolers for cpus here is the official answers from Noctua about NH-D15/U14S/U12S (motherboard Asus Z10PE-D8-WS):
Two NH-D15 cooler are indeed a quite heavy load for a mainboard, especially on LGA2011 where the coolers are installed on the socket ILM and not on a backplate of our own design. While it would probably work, personally I would rather stay away from it and opt for smaller heatsinks or take some measures to easy the strain on the mainboard.
Apart from that you will run into troubles if you must use the first PCIe x16 slot.
Even with a smaller cooler like the NH-U12S you are not entirely trouble free as it would limit the available length for cards in the first slot.
If this is not an issue for you, then you can either take the NH-U12S, which should be sufficient for these processors with good case ventilation in place, or the NH-U14S (same width as the NH-d15) which has similar performance than a NH-D15 at stock clocks but is a bit lighter.
Regardless of the cooler you actually choose, if you are going to transport the system between different places and not just from one room to another I would recommend to remove the coolers for transport.
Kind regards,
Andreas Karner
Noctua support team