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