15. \(2\frac{2}{3}\cdot1\frac{1}{31}\)

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

\(\frac{8}{3}\cdot\frac{32}{31}=\frac{256}{93}=2\frac{70}{93}\).

Ответ: \(2\frac{70}{93}\)