15. As shown in the figure, a cylindrical container with a base diameter of 10 centimeters is filled with water. First, a conical iron block with a base diameter of 8 centimeters is placed into the container, and the iron block is completely submerged in the water. Then, the iron block is removed, and the water level drops by 3.2 centimeters. The height of the conical iron block is $\qquad$ centimeters.
【Solution】The volume of the conical iron block is:
$$
\begin{array}{l}
3.14 \times(10 \div 2)^{2} \times 3.2 \\
=3.14 \times 25 \times 3.2 \\
=251.2\left(\mathrm{~cm}^{3}\right)
\end{array}
$$

The height of the iron block is: $251.2 \times 3 \div\left[3.14 \times\left(\frac{8}{2}\right)^{2}\right]$
$$
\begin{array}{l}
=251.2 \times 3 \div 50.24 \\
=15(\mathrm{~cm})
\end{array}
$$

Answer: The height of the iron block is $15 \mathrm{~cm}$.