iMac 27" Late 2015 A1419 4K - SLOW Fusion hard drive replacement with new internal SSD, MUCH FASTER! - YouTube
Amazon.com: Timetec 1TB MAC SSD NVMe PCIe Gen3x4 3D NAND TLC Read Up to 2,200MB/s Compatible with Apple MacBook Air(2013-2015, 2017), MacBook Pro(2013-2015), iMac(2013-2019), Mac Pro(2013), Mac Mini(2014) : Electronics
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac
How to add a fast new SSD to your old Mac or MacBook for only $150 - 9to5Mac