Fifteen
Old English fīftēne, fīftīene (see five, -teen).
wiktionary
From Middle English fiftene, from Old English fīftīene, fīftēne, from Proto-Germanic *fimftehun. Cognate with West Frisian fyftjin, Dutch vijftien, German fünfzehn, Danish femten.
etymonline
fifteen (adj., n.)
"1 more than fourteen; the number which is one more than fourteen; a symbol representing this number;" Old English fiftyne, from fif "five" (from PIE root *penkwe- "five") + tyne (see -teen). For vowel shift, see met (v.). 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 (from quinque "five;" see quinque-; + -decim (see -teen). The number of players forming a side in rugby.
