It directly depends on the upload speeds of the people you're downloading from. I assume you understand how bittorrent works. (i.e. if everyone torrenting the file is on a 56k, you won't get fast downloads, you're downloads will only be as fast as the sum of the upload speeds from your peers).
Yeah, and one reason why you might be getting so low dl speeds is because there are so many leachers around that steal all the speed while giving none.