$15k!
You have to ask yourself if you want to drop that kind of money on consumer GPUs, which launched late 2022. But then again, with that kind of money you are stuck with consumer GPUs either way, unless you want to buy Ada workstation cards for 6k each and those are just 4090s with p2p memory enabled. Hardly worth the premium, if you don't absolutely have to have that.
which means you could build a 4gpu server from normal cases.
most of the 4090 cards are 2-3 slot cards
so you are getting a better practical card for the price
if you are making a mining type rig, then yeah, the extra price is wasting money.
but if you wanted to build a normal machine, the workstation cards are the most reasonable choice for anything more than 2 gpus
Only if you are already live near an airport and you are accustomed to the sounds of the lift off and flying away.