How long does a memory foam mattress like this last?

This one is built to outlast most foam beds, scoring 9.5/10 on durability with a 15-year warranty. The comfort layer where impressions normally form is genuine high-density 4 lb foam, not the cheap low-density foam that troughs within a year or two, sitting on a dense 8-inch core that holds its shape. Keep it on solid, even support, rotate it occasionally, and use a protector, and it will hold up for many years without sagging.