Jim Walton was ranked at # 15 on the Forbes list of world billionaires before 2011 .
His brother John Walton 's widow Christy Walton , his sister Alice Walton , and his brother Rob Walton were all listed at # 12 with a net worth of US $ 17.6 billion each.. He was ranked at # 15 on the March 2012 Forbes list of world billionaires with a net worth of US $ 20.7 billion .