-85% is the change from 100 to 15
Calculation steps:
[( 15 - 100 ) ÷ 100] x 100 = -85%
Formula
Percentage change = [(15 - 100) / 100] x 100
Subtract the new number by the original number
15 - 100 = -85
-85 ÷ 100 = -0.85
-0.85 x 100 = -85%
Example