You’ll miss the fine points, but after a few minutes, you’ll get the main ideas. You already know something of the subject matter and that makes it easier. And, besides, no one cares if you didn’t understand it anyhow.

Have patience with yourself. Let your ear become accustomed to the Spanish. It’s similar to watching a British drama on TV. At first, British accents and expressions are a jumble, but slowly it becomes comprehensible. You still have to maintain your attention. Some effort is necessary. So it is with Spanish.