The circumference \( C \) of a circle is calculated using the formula:
\[ C = 2\pi r \]
where \( r \) is the radius of the circle. Given that \( r = 15 \) mm, you can substitute this value into the formula:
\[ C = 2\pi(15) \approx 2 \times 3.14 \times 15 \approx 94.2 \text{ mm} \]
So, the approximate circumference is about 94.2 mm.