As a young adult recruit, I came in from a background of "speak when you're spoken to; answer what you're asked" so it was torture to be told that I had to join the Ministry School, even as a "householder."
I don't know when that changed, I know it was years later, but it got to the point where I could walk into the Hall two minutes before meeting time, be told that they needed someone to give the #3 or #4 talk, and I'd pull one together in about five minutes using one of my older kids as householder. There wasn't really anything to it, the material was simple enough and, as you said, the situations are so fake that I didn't have to spend any time making the thing look realistic!
What changed was my confidence level. At first I thought I actually had to know something, maybe even more than those in the audience. My fear began to dissipate when I realized that most of the people weren't even listening and that nobody remembered who said what by the following week. Giving a talk became as mundane as doing the laundry or shopping for groceries.
It helped me to be in the School. One less "mountain", one less obstacle to overcome! Later, when I took a class in Public Speaking or had to give presentations at work, my stress level was 'way down; I could concentrate on articulating and defending my position.
One of the times that I was consciously grateful for the Ministry School was during a class on International Business. Each student had to choose a "controversial" case to present and defend. Unbeknownst to me, the instructor, an attorney, had an entirely different perspective on the case that I chose and proceeded to devil me, the like of which we had never seen in that class. It was a tennis match for a while, but eventually he stopped. I was still prepared for another round! As I walked to my seat someone in the class called out "You go, girl!" I was stunned. Long way from being afraid to open my mouth, eh?