iMac with Retina 5K Display 2014/2015 Memory Upgrades
Can you upgrade the RAM in the 27-inch iMac? | iMore
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