How is it possible, AMO executed at Pre Market session?

Is it possible that if i place an AMO previous day, it gets executed before market opening time 9:15 ??

Yes, Happened with me a lot of time. You placed the best price.

Chances are there if there is opposite order there for you.

most of my AMO orders are executed before market opening.

If not executed AMO order will be converted as Limit order with open price.

50 % of those Limit orders will be executed at 9:15 AM.

Whatever? If the market is not even open for trade, how order gets executed ?

AMO are converted into order at 9.00 am and first order execution happens at 9.07 am. It seems your price match the corresponding order and so it got executed at 9.07 am.