You couldn't actually build a standard computer for 15k unless you were just trying to spend money, it'd have to use server parts.
For example; 4 titans is 4k, a 4970x (I think that's the model number) is ~1k off the top of my head, motherboard 500, case 500, psu 400, ssds 2k (why not lol), os 200. That's 8.6k.
Now if you wanted 3 4k screens to go with it, that would make it ~17k I think, but you get the point. I'm not even sure if you can use 3 4k screens at once