Which number is greater: 15 or 18?

To determine which number is greater between 15 and 18, we need to compare the two values directly. The number 18 is larger than 15 because, when counting in ascending order, 15 comes before 18. In numerical terms, 18 is four units greater than 15. This makes 18 the greater number in the comparison.

Considering the other options, 15, 17, and 16 are all less than 18, making them not applicable for this specific question about which number is greater between 15 and 18. Only 18 meets the criteria of being larger, affirming that it is indeed the correct answer.