Your cooler might block RAM, but not because of DDR5.

It depends on the specific motherboard, not the memory type. DDR5 sticks are physically the same size as DDR4—same height, same width. The clearance issue with a chunky cooler like the NH-D15 has always been about how far the heatsink overhangs the DIMM slots. That hasn’t changed.

What has changed is motherboard layout. Some DDR5 boards move the CPU socket slightly or shift the DIMM slots closer to the socket. It’s rare, but possible. The real variable is whether your board has the first DIMM slot tucked under that massive front fan on the NH-D15. Noctua keeps a compatibility list on their site—check it before you buy anything.

If you already have the board and the cooler, you can usually work around it: move the front fan up (costs a few mm of clearance), or just use the middle fan only. Works fine. Or get low-profile RAM. But first: check that compatibility list.