No. Apple releases an updated iPhone every year. People who don't know that already aren't going to be paying attention to the announcement. People who do know and care aren't going to be buying iPhones after March.Wouldn't that kill sales of iPhones leading up to the "pre-announced" iPhone? That just seems like a foolish business decision. If it was Samsung on the other hand...
Maybe you really are saying that you are waiting until March to buy the iPhone 7, because you really want it, but if you find out Apple will have a new iPhone in September you probably won't do it. If so, I have news for you. Apple will probably be releasing a new iPhone in September. The iPhone 7 won't be the last model Apple makes.