OWC 16GB (2 x 8GB) PC14900 DDR3 1866MHz SO-DIMMs Memory Compatible with 2015 (Late) iMac 27" w/Retina 5K Models and Compatible PCs (OWC1867DDR3S16P) at Amazon.com
16GB 2 x 8GB 1866 1867 MHz PC3-14900 Memory RAM for Late 2015 APPLE iMac 5K 17,1 | eBay
UVU Surplus on Twitter: "I mac 27 inch all in one desktop year: late 2015 memory: 8GB DDR3 1867 MHz screen: Retina 5k video card: AMD Radeon R9 M380 2048MB HD: 1T