Its never too early to start the preparation. Please get hold of the course material for the entrance exam. Identify your areas of strength and opportunities. Seek support on the areas that you find difficult. Join online forums frequented by TISS Students to get a better view.
The best part is, not just you would utilise your time for a better future, you are going to be far ahead of your competition.
Wish you all the best!
It is nice to have an ambition to join a famous institution like TISS.
Work towards it.
Anything worth achieving needs hard and harder work.
But one small line in your post ""I beleive that this would grant me a huge amount of free time. ""
needs to be viewed in holistic manner.
Why are you looking at free time?
This is the age when you should be involved all the time to develop knowledge,personality and fully as young man.
You should have an educational road map tied to your overall objectives in life.