Discovery is raising $1.5 billion in new debt through a public offering, in part to repay or refinance other debt, according to a SEC filing made public Thursday. The new debt raise includes $640 million in senior notes at 4.375 percent interest, due 2021, another $496 million in senior notes at 3.3 percent interest and due 2022, and $345 million in senior notes at 3.5 percent interest, and due 2022.