In inverse variation, the relationship between \( x \) and \( y \) can be expressed as:
\[ x \cdot y = k \]
where \( k \) is a constant.
First, we need to find the constant \( k \) using the provided values \( y = 20 \) when \( x = 15 \):
\[ k = x \cdot y = 15 \cdot 20 = 300 \]
Now that we have \( k = 300 \), we can find \( x \) when \( y = 5 \):
\[ x \cdot y = k \implies x \cdot 5 = 300 \]
To find \( x \), we can rearrange the equation:
\[ x = \frac{300}{5} = 60 \]
Thus, when \( y = 5 \), \( x \) is \( \boxed{60} \).