Step 1: Write down the given numbers:
15, 6, 16, 8, 22, 21, 9, 18, 25.
Step 2: Arrange the numbers in ascending order:
6, 8, 9, 15, 16, 18, 21, 22, 25.
Step 3: Find the median. Since there are 9 numbers (an odd number), the median is the middle number in the list.
The 5th number is 16.
Thus, the correct answer is \( 16 \).