To simplify \( 5^{10} \cdot 5^5 \), we can use the Product Rule of Exponents, which states that when you multiply two powers with the same base, you add their exponents:
\[ a^m \cdot a^n = a^{m+n} \]
In this case:
\[ 5^{10} \cdot 5^{5} = 5^{10 + 5} = 5^{15} \]
So the simplified expression is:
\[ 5^{15} \]
Thus, the correct response is:
\( 5^{15} \)