quindecennial

quin·de·cen·ni·al

 (kwĭn′dĭ-sĕn′ē-əl)
adj.
1. Occurring once every 15 years.
2. Lasting 15 years.
n.
A 15th anniversary.

[From Latin quīndecim, fifteen; see penkwe in Indo-European roots + Latin -ennium (from annus, year; see at- in Indo-European roots).]

quindecennial

(ˌkwɪndɪˈsɛnɪəl)
adj
occurring once every 15 years or over a period of 15 years
n
a 15th anniversary
[C20: from Latin quindecim fifteen + annus year, on the model of biennial]
References in periodicals archive ?
Key-in quinquennial for a fifth, decennial for a tenth, and quindecennial for a fifteenth.