fifteen (n.) Look up fifteen at Dictionary.com
Old English fiftyne, from fif "five" (see five) + tyne (see -teen). Cognate with 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).