On the number line, smaller numbers are located to the left of larger numbers, which are located on the right.
So, if you have two numbers x and y on the number line, the smaller of the two will be on the left, the larger one on the right.
So, -13 is located to the right of -15, because it's larger.
For the same reason, -11 is located to the right of -13.
On the number line, you would have something like
<--------(-15)-------(-13)--------(-11)---------->