But SSDs that cost the same as a 15K disk do not have anywhere near the life time of the spinning disk due to write endurance limits.

So load half a billion rows but don't update it too often!

SSDs live long enough. You get magnitudes more IOPS performance out of a single SSD than a RAID of 15k disks, it consumes magnitudes less power, it costs less, and it needs less maintenance. It's a complete no-brainer these days to put an SSD in your database server.

Given the cost of power and space and vs. the number of additional drives necessary I'm not sure that longevity is worth it.