Simple , you need 1,985,340 XP to level up from 150-151 but you need almost x10 that from 200-201 ( 12,238,786) to be precise.
I will give you a perfect example:
Colombian set is the best for XP + Labor points for players that dont have any other XP set ( I mean other combinations that give you more XP ) so with Colombian set you need 90 days to reach 150 if you do 8 hours of 15s every day. Bare in mind the buffs needed too. This is calculated by 130 XP per 15s but since you level up and with Colombian set you will be able to do better jobs later on at 120+ so give or take around 75-80 days to reach 150.
Now the same for level 200 , you need to farm 8 hours of 15s every day for 3 and half years , maybe 3 years because of the better jobs later on that give better XP.
To go from 150-151 you need around 3-5 days with farming 8 days + login bonus , but from 200-201 you need 40 days + login bonuses and with jobs that could give you 180-200 xp per 15s. Totally fair right?
The xp should be increased by 25 for every 3-5 levels you level up imho.
For better visual of XP table , this is all the XP needed for each level
https://wiki.the-west.net/wiki/Experience