Apple iMac 5K Retina 27" Desktop - 3.2GHz Quad-Core i5 - 16GB RAM - 1T – The Refurbished Apple Store
Install memory in an iMac - Apple Support
iMac Retina 5K: Memory upgrade (RAM)
Upgrade RAM on Apple Retina iMac 5K (Late 2015) / How To install memory - YouTube
Apple 21.5" Certified Refurbished iMac Desktop Core i5 1.6GHz 8GB Memory 1TB HDD (2015) Silver MK142LL/A - Best Buy
OWC 8GB (2 x 4GB) PC12800 DDR3L 1600MHz SO-DIMMs Memory Compatible with 2011-2015 iMac, 2011-12 Mac Mini, and 2011-2012 MacBook Pro (Non-Retina Display) Models (OWC1600DDR3S08S) at Amazon.com
Install memory in an iMac - Apple Support
Amazon.com: Late 2015 Apple iMac with 3.2GHz Intel Core i5 (27 inch Retina 5K, 8GB RAM, 256GB SSD) Silver (Renewed) : Electronics
iMac RAM Upgrade 8GB-32GB (Late 2015) - YouTube
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
Install memory in an iMac - Apple Support
A-Tech 8GB RAM for Apple iMac Late 2015 27 inch Retina 5K | DDR3L 1866MHz / 1867MHz PC3L-14900 1.35V 204-Pin SODIMM Memory Upgrade Module at Amazon.com
Amazon.com: Apple iMac MK462LL/A 27-inch Desktop Intel 5K Display 16GB Ram | 1TB Hard Drive (Renewed), Mac OS X : Electronics
OWC Tears Down iMac Retina 4K, Confirms Memory Is Soldered