1) – you don’t need the apostrophe in ‘clown’s’. It’s a plural. 2) No – class clowns are often good at zingers or quips or in-the-moment sort of quick remarks. You know, the sort of smartass remarks that gets them into trouble. Public speaking is most often reading from a script, or at least from an outline and talking points, meaning that you lay out your subject, give evidence to support what you’re saying, and then need to wind up with a persuasive repetition of your point. Totally different skills.