I'm not so sure about this. I have a problem believing that the eccentric orbit of a planet this size would not have disrupted the Earth orbit by now. 15,000 year orbits go by pretty quick on a solar system scale. There would have been so many opportunities for a close pass to have pulled Earth out of it's current orbit by now. All scientific evidence shows that the earth has had a stable orbit for the past 3 billion years, since the gigantic collision that formed out moon from the Earth impact debris.
I called my brother-in-law, Michael Cassutt, author, space historian, and guest speaker on many-many Discovery, Nova and History channel contributing expert. This guy knows his stuff, he's one of the guys the networks call and then put on TV when they need an outside expert commentator.
He laughed and said, "Yes I know what you are talking about and the entire theory is not only ridiculous but also impossible. It would have disrupted the solar system and we would not be here."
But hey, you guys are having fun, don't let the laws of physics and celestial mechanics stop you now.