This is an interesting discussion. The prologue i have written for my current project (climate fiction/fantasy) is 2200 words. It feels long to me, but I like it.
I saw writing it as a way to provide supplemental info, as Nicole says. It complements the story and takes place 17 years before. It fleshes out two characters that have less play in the main text.
I loved writing it, and I like it. It complements the story. And I see prologues and epilogues in fantasy. But about half the people I see/share with say to ditch it.
Since we live in an age of webpages I am thinking of putting some of these things on a website for anyone who starts to nerd out on my world. I like the idea of weaving the essential info in. But, I gotta say, I still aesthetically like the idea of a section of the book that provides a different feel.
This is not so much an answer as a response to the thoughts here which are along the lines of "here's my experience." My experience is I love my prologue but 50% of the people I share with, don't. If publishers don't want it, then I think it makes sense to build a website and push my (fantastic) manuscript with the teaser that a website adds supplemental info.