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