Dear Aspirant,

As there is only 15 months for preparation of IIT JEE mains for you, the exam can be done with proper strategy while doing every small things correctly and consistently everyday.

-->First thing one should have a very strong planning for each and every day, week and month for all subject. Obviously make a proper routine and try to follow it with efficiency.

-->Try to do as much question as you can daily and while doing these have a timer with you, it would give some time pressure and train your brain for exam mode. If you do it consistently then in all exams you won't  face much time pressure.

-->Try to figure out areas you are weak in and try to overcome the weakness with proper guidance whether it can be online/offline.

-->Also try to give mock tests in every months two to three times and analyze your paper, look for mistakes and write them down somewhere, with this you won't repeat them and you'll  learn from them.

You should be well acquainted with all concepts in all subjects so that in exam you know which question to skip and which to solve. There's  no point in investing a lot of time on a question you are uncertain about. On final day each and every minute matters.

Also check out these link which might help you in preparation;

https://engineering.careers360.com/articles/how-prepare-for-jee-main

https://engineering.careers360.com/download/sample-papers?sort=recommended

Hope it helps you..

Best of luck..