If it can't be read from the back of the room, make it bigger. There is a tendency to project too much onto the screen at once. Audiovisual aids are meant to be key points, outlines, maps, cross-sections, diagrams. Audiovisual aids are not meant to be text. Don't read your powerpoint screen or turn away from the audience to read what you are projecting.
Some speakers have a major problem with timing.
Often this time limit includes time for questions and discussion. Don't be a person who hasn't even made your main point when time is up. Use the time allowed or slightly less. Fifteen minutes does not mean 20 or even 16 minutes. Practice your presentation to friends.