quintus-dĕcĭmus, a, um, num. adj.,
the fifteenth (class.): locus, Cic. Inv. 1, 54, 105: quintisdecimis castris, Liv. 45, 33 fin. : in libro quintodecimo, Gell. 1, 16, 11; often separately: quinto decimo Kal. Dec., Col. 11, 2, 88; and sometimes in reverse order: anno decimo quinto, Eutr. 1, 19.