iMac with Retina 5K Display 2014/2015 Memory Upgrades
16GB -2x8GB Memory Ram Upgrade for 27" Apple iMac-15.1 Core i5 3.3GHz Mid 2015 | eBay
timetec hynix ic 16gb kit(4x4gb) compatible for apple ddr3l 1600mhz pc3l-12800 for imac(mid 2011, late 2012, late 2013, late 2014 retina 5k, mid 2015 retina 5k) sodimm memory upgrade|max slots upgrade - Walmart.com
Install memory in an iMac - Apple Support
4GB PC3-12800 RAM for Apple iMac Mid 2015 - 27 Inch Retina 5K MF885LL/A - MF885xx/A Memory Upgrade Module