In order to keep your adudience interested your speech should have complexity t or f

This is true.

If your speech lacks complexity and details, your audience will likely find it boring and uninteresting. If the speech contains clear details and is spoken with a strong tone, it will more strongly grasp your audience's attention.
The audience is more interested in learning about a new topic or argument from your speech, and they will find your speech/presentation uninteresting if you are unable to clearly explain your viewpoint or facts.