To simplify the fraction \( \frac{15}{100} \), we can divide both the numerator and the denominator by their greatest common divisor (GCD).
The GCD of 15 and 100 is 5.
Now, divide both the numerator and the denominator by 5:
\[ \frac{15 \div 5}{100 \div 5} = \frac{3}{20} \]
So, \( \frac{15}{100} \) in simplest form is \( \frac{3}{20} \).