What do you think of this prolouge opening? Can you give any ideas to make it a bit longer?

I think that your prologue is intriguing; it does seem unfinished, however, requiring some sort of resolution to the second part involving Ivan, I would think. You just end that without even any punctuation. I think that you might include a fourth segment where you make a further reference to his memories. You do, too, have a few errors in what you've written, although predominantly it is well done. Where you wrote contexts, I think that you meant contents, actually. Also, you spelled Nedble as Nedlbe a couple of times; that second version would be fairly unpronounceable, so do you use Nedble. Where you write I. S, you need a period to follow the S, too. So far as context is concerned in what you've posted, you piqued my interest; I'd like to know where your story is going. My advice: Keep writing! I am wondering why what you've excerpted here is a prologue; what will be the main body of the story? Prologues aren't always necessary. Anyway, your beginning has hooked me. Good luck with the continuation!