-97.75% is the change from 666 to 15
Calculation steps:
[( 15 - 666 ) ÷ 666] x 100 = -97.75%
Formula
Percentage change = [(15 - 666) / 666] x 100
Subtract the new number by the original number
15 - 666 = -651
-651 ÷ 666 = -0.9774774774774775
-0.9774774774774775 x 100 = -97.75%