How you must lose same %?
Example:
In 1.5 you had to farm 100 exp till level 77.
In 2.0 you had to farm 150 exp till level 77.
I farmed 25 exp in 1.5 I had 25%. In 2.0 I will have 16.6% ( 150/25 = 6, 100%/6 = 16.6 ), 25-16.6 = 8.4% difference.
You farmed 70 exp in 1.5 you had 70%. In 2.0 you will have 46.7% ( 150/70 = 2.14, 100%/2.14 = 46.7 ), 70-46.7% = 23.3% difference.