Im doing something terrible wrong?
Or what?
the scene is HUGE, there are 17000 lights, all of them IES, and I did only 3 minutes render
Looks like so. If the scene is larger than what we see in this image, simply separate it into other scene, or just isolate.
If you need 17k lights, than you're probably choosing inneficient way of creating this light array. There is always possibility in CGI to have visually identical result, while having vastly optimized way how to achieve it.
At this point, perhaps screenshot would help.