fifteen (n.) Look up fifteen at Dictionary.com
Old English fiftyne, from fif "five" (see five) + tyne (see -teen). Cf. Old Saxon fiftein, Old Frisian fiftine, Old Norse fimtan, Swedish femton, Dutch vijftien, German fünfzehn, Gothic fimftaihun "fifteen." French quinze, Italian quindici "fifteen" are from Latin quindecim (see Quatorze).