15. \(2\frac{2}{3}:1\frac{1}{31}\)

\(2\frac{2}{3}=\frac{8}{3}\), \(1\frac{1}{31}=\frac{32}{31}\).

\[\frac{8}{3}:\frac{32}{31}=\frac{8}{3}\cdot\frac{31}{32}=\frac{31}{12}=2\frac{7}{12}\]

Ответ: \(2\frac{7}{12}\)