Hi aspirant

As you said you coverd 15% of your syllabus so 85% of your syllabus you want cover within 3 months. It is little difficult to cover all three subject within three months but not impossible if you have to work very hard to cover it because all three are main subject. So for cover the whole syllabus you have to study 10-12 hours in a day. For each subject you have to give a particular time like for mathematics 3 hours for physics 3 hours for chemistry 3 hours. Try to cover a chapter within 1-2 day for each subject and revision the chapters. Choose a particular day in a week for revision for better result otherwise you forget previous chapter. For organic chemistry you have to practice every day I mean yesterday if yesterday you study a reaction practice it today otherwise you forget it. If you study properly so it is not too difficult for.

I hope it helps you.

Best wishes.

Hii!
For whatever exam you are preparing and want to finish the class 12th syllabus in just three months, let me tell you, that will only happen if you are determined and regular in your work. You need to be consistent in studies and stop procrastination. Divide your syllabus and know what is difficult and easy for you. Give more time to the Subjects you feel tough and then give time to easy subjests. Eat the frog first. This means, complete the hardest task of the day day first. Complete the daily task of tough Subject first and then, as the day progresses, move towards the easy ones. Solve previous year question papers and revise every day.
To stay focused, practise meditation, exercise, yoga etc., Have healthy diet and sleep well, on time.
Hope this helps.
Good luck!