It is a rational number because it is a fraction of two integers. Those two integers being -15 and 2.
In general, any rational number is of the form P/Q where P and Q are integers. The Q cannot be zero. Another example of a rational number is 2/3. In this example, P = 2 and Q = 3.
Going back to -15/2, we would have P = -15 and Q = 2.
The fraction -15/2 is not a whole number nor is it an integer. This is because -15/2 = -7.5 and this is sufficient to see we don't have an integer result. We would need to have nothing after the decimal point to get a whole number.
