State Marriage Defense Act of 2015
Prohibits, in determining the meaning of any Act of Congress or of any ruling, regulation, or interpretation of U.S. administrative bureaus and agencies as applied with respect to individuals domiciled in a state or in any other territory or possession of the United States: (1) the term "marriage" from including any relationship that the state, territory, or possession does not recognize as a marriage; and (2) the term "spouse" from including an individual who is a party to a relationship that is not recognized as a marriage by that state, territory, or possession.