To simplify \( 5^{10} \cdot 5^{5} \) using the Product Rule of Exponents, we can add the exponents since the bases are the same.
The Product Rule states that \( a^m \cdot a^n = a^{m+n} \).
Applying this to our expression:
\[ 5^{10} \cdot 5^{5} = 5^{10+5} = 5^{15} \]
Therefore, the correct answer is:
\[ 5^{15} \]
So the response would be \( 5^{15} \).