The best way to prepare a presentation is to practice on a complete (but intelligent) outsider. Even (maybe especially) if your audience consists of industry experts.
You see this often in pitches of technology startups to venture capitalists for fund raising. The entrepreneur is an expert. The VC audience knows a thing or two about technology. Buzz words, generic truths, and jargon fly through the room. The message did not come across...
Any intelligent person should be able to understand your story in 15 minutes, even if she does not have any background in your specific field of expertise. If she does not get the point, it is your fault, not hers.

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