Hi and welcome!
I did lose 15 lbs in the first two weeks of doing FF. Everyone's body reacts differently to the program though so if you don't hit the 15 lb mark after the first two weeks do not give up! Take note on how much better you feel eating the FF way!
I found I only experienced a caffine withdrawl headache for one day.
I really like this program and eating the way I am now.
Good Luck!