Old 10: 100*1.1^9 = 236%(+136%)
New 10: 135*1.1^9 = 318%(+218%)
Old 13: 100*1.1^12 = 313%(+213%)
New 13: 135*1.1^12 = 423%(+323%)
Old 15: 100*1.1^14 = 380%(+280%)
New 15: 135*1,1^14 = 513%(+413%)
Old 18: 100*1.1^17 = 505%(+405%)
New key difficulty equals to a ~3 levels higher old key
Also fun is the comparisson between the very first +10 difficulty vs. the +10 difficulty nowadays.
First +10: 100*1.08^9 = 200%(+100%)
7.3 +10: 205*1.10^9 = 483%(+383%)