To rewrite \( 15^{-38} \) using positive exponents, you can apply the property of negative integer exponents, which states:
\[ a^{-n} = \frac{1}{a^{n}} \]
Applying this to \( 15^{-38} \):
\[ 15^{-38} = \frac{1}{15^{38}} \]
So, the expression with positive exponents only is:
\[ 15^{-38} = \frac{1}{15^{38}} \]