It's amazing to think of the rapid rate that Sir Walter accumulated his debt. While Lady Elliot was alive, they lived within their means. I think it's safe to assume that his income was not reduced -- if so, I think Jane Austen would have mentioned it. So, in fourteen years, Sir Walter racked up so much debt that it will take him 7 full years to pay it off. To do that, he needs to rent his house, eliminate many servants, relinquish his horses, etc.