iMac RAM for Model 13.2 to 15.1| DDR3-1600MHz | 8GBx2 | MacMemory.com
Amazon.com: Adamanta 16GB (2x8GB) Apple Memory Upgrade Compatible with Late 2015 iMac 27" Retina 5K Display DDR3/DDR3L 1867Mhz PC3L-14900 SODIMM 2Rx8 CL13 1.35v RAM DRAM : Tools & Home Improvement
CMS 16GB (2X8GB) DDR3 14900 1866MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I5 3.2 27" (5K, Late 2015) Mk462Ll/A - A5 at Amazon.com
upgrade - Optimal Memory Layout for Late 2015 iMac - Ask Different
16GB -2x8GB Memory Ram Upgrade for 27" Apple iMac-17.1 Core i5 3.2GHz Late 2015 | eBay
Install memory in an iMac - Apple Support
64GB Memory Upgrade for late 2015 iMac
Apple iMac review (21.5-inch, 2015): 4K is optional, faster hard drives shouldn't be | Engadget
Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3L 1600MHz PC3L-12800 CL11 for iMac (Mid 2011, Late 2012, Late 2013, Late 2014 Retina 5K, Mid 2015 Retina 5K) SODIMM Memory Module MAC RAM Upgrade at Amazon.com
New 21.5-inch iMac least repairable yet due to lack of RAM, hard drive upgradability - 9to5Mac