Any link to the 15k machine ?. Maybe it is cheaper now.
If 4 GPUs connected via PCIe 4.0x16 are enough you can choose among various sRTX4 boards for 3000 series AMD Threadripper CPUs.
[§] https://www.reddit.com/r/deeplearning/comments/tw0olq/commen...
Another useful URL: https://www.pugetsystems.com/labs/articles/Quad-GeForce-RTX-...