You can actually starve tame these for a faster taming you just have to wait 1-2 seconds. Put the berries in your last slot and just wait for it's food to go down then you can add the berries practically one after the other :) also make sure it's inna taming pen and is able to starve and not find food out in the open.
It literally only took me an hour to tame a level 145 with only 50 mejoberries.
1. Gather berries and put the berries in your last slot
2. Kneel down and walk up to one of them and feed it the berries
3. Now you just follow it around while kneeling down and feeding it berries whenever it's hungry
4. Congratulations you tamed one.
Since they're commonly found in the red wood forest, I recommend only taming one if you're close to water as if you get attacked by something you can jump into the water to get away. Then when you think it's safe just go find your monkey and go back to following/feeding it.