(physics) A stable isotope of nitrogen, ¹⁵₇N, having seven protons and eight neutrons; it accounts for less than 0.4% of the natural element; it is used in nuclear magnetic resonance spectroscopy

Ellipsis of 15 minutes of fame.

Alternative form of sweet fifteen

plural of AR-15

(trademark) A lightweight, semi-automatic rifle, based on the original design of the ArmaLite AR-15.

(US, Canada, colloquial) Alternative form of freshman fifteen

plural of sweet 15

A sliding-block puzzle with 15 sequentially numbered square tiles in a 4×4 frame, the aim being to arrange the numbers in order by sliding one at a time horizontally or vertically into the single available space.

plural of 15 puzzle

(idiomatic) A very short time in the spotlight or brief flurry with fame, after which the person or subject involved is quickly forgotten.