Let's call the starting value 'x'

Let's call the final value 'y'

x * 1.15 will give you the 115% (your 115 value)

(x * 1.15)*(0.85) will give you 15% off the value of 115% (your 97.75 value)

So, you can write the expression as:

1.003x = y

What you seem to be asking for is bizarre, as you would simply be multiplying by 1.