Originally, only one person in the synagogue was honored with saying the Kaddish, but eventually every eligible mourner made his way onto the scene. Problem is, with more than one mourner saying Kaddish, the result could sound more like a noisy flock of Aramaic geese. The main point of the exercise, as we've explained, is not to say the Kaddish, but that everyone should answer. It's hard to answer ten geese all on different tracks. So getting everyone in synch is of key importance.
Many synagogues ask that all the mourners line up together. Others tell you to please follow the prayer leader. If you find you can't keep up, try standing close to the others and read louder, so they'll notice and slow down. People are usually considerate about these things. Never be embarrassed that you're going too slow. It's a house of prayer, not a racetrack.