Schooling for Year 11/12 - Public or Private?

Hi everyone,
I live in Sydney and i've been attending a private school for all of my schooling up until this point. Recently however, i was accepted into a selective public school.
So i'm facing a bit of a dilemma - im not really sure if i should bother changing schools with only two years left to go, or if im making a huge mistake in just not accepting the position i've been offered straight off.

I was accepted into a school i didnt think i would be accepted into, as i applied late and it's a very very good school (well from what i've read anyway...).
So i'm wondering why on earth im hesitating...
And i think it's probably because of a few reasons - i dont really know much about how the school itself works firstly, im worried about being extremely far behind in the work compared to the students attending the school already, and i feel compelled to stay where i am established and comfortable.

So any suggestions of pros/cons in relation to changing schools which could add to my considerations whilst i make this decision are indeed appreciated.

Thank you in advance.