It's terrifying if you're not used to it, for anyone really. It's stressful because you're the centre of attention, everyone staring at you, taking notes on what you say. You've got to remember what to say, you've got to use up the right amount of time without being able to just stare at a clock, people might ask questions you don't know the answer to. Did you know that even people who don't stutter still worry about being disfluent when they give speeches? That feeling of "oh god, what if I can't get my words out, what if I trip over them and everyone thinks I sound stupid"? Yeah, that's not unique to people who stutter, a lot of people get extremely stressed about that. It gets easier the more you do it, though.