If you embroider your facts with the stories and support that will make them memorable, chances are you will have too much to say. Condensing a speech you've worked hard on into the allotted time may seem cruel, unusual, and impossible. But it's necessary. When you take time to condense your speech, your audience is much more likely to listen to what you say, because long-windedness leads to repetition and lack of focus.
It takes time and thought to condense everything you know about a subject into a few highly refined major points. Woodrow Wilson, the last president to write his own speeches, was once asked how long it took him to prepare a 10-minute speech. "Two weeks," he said. And how long for an hour's talk? "One week." And for a two-hour presentation? "Oh," he said, "I'm ready now."