Subtract.

-15-6=

-15 - 6 = -21

To subtract -15 from -6, you would follow these steps:

Step 1: Write out the equation: -15 - 6

Step 2: Start with the number -15.

Step 3: Subtract 6 from -15.

-15 - 6 = -21

Therefore, -15 minus 6 equals -21.