A prime number has exactly two whole number factors, 1 and itself.

A composite number has more than two whole number factors.

Express the number 15 as a product of its factors.

Write the factors of 15.

15 = 1 × 15.

15 = 3 × 5.

Factors of 15 are 1, 3, 5 and 15.

Since 15 has more than two factors, it is composite.

The number 15 is a composite number.