It’s not possible dude
It’s better you study 12 hours a day
Because after studying for 15 hours a day you will get saturated in one week and you will end up wasting your whole day as nothing will enter your brain
So study for 10 hours in the beginning and increase to 12 to 13 hours in last month before exams
Pls make sure to take breaks every two to three hours depending on your concentration
I used to do mediation by putting my head phones
For ten minutes every three hours you can choose anything else also depending on what you like
And take daily bath good food and half hour of brisk walk exercise is must for your brain