how much preparation do i need for the toefl ibt?

English isnt my native language,but i've been having english at school for about 10 years, and every summer i go to a summer camp in the states or uk for like a month, i read english everyday and listen to it daily, but what kinda worries me is the speaking part, because you only have 15 seconds to prepare it and there's like everybody talking at the same time, any advices?</p>