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