To find the median of a set of numbers, you first need to arrange them in order (which they already are in this case) and then determine the middle value.
The data set you provided is: 7, 8, 9, 10, 11, 15.
Since there are six numbers (an even quantity), the median will be the average of the two middle numbers. The two middle numbers in this set are 9 and 10.
To find the median: \[ \text{Median} = \frac{9 + 10}{2} = \frac{19}{2} = 9.5 \]
Therefore, the median is 9.5.