As I said in that other thread; I like the video, but I will put my head out and say: 15 000? Forget it!
Honestly, I don't even think you will make 10 000. Not because I don't think you are able to do it. I saw your 7000 people settlement! You are very well able! But the game is so full of bugs, as it grows bigger. The mods doesn't help here either. My experience is, that itīs getting much worse with mods. So I don't think it could be done. I do hope I'm wrong! If I can do anything to help you prove me wrong, I'll be glad.