With a passphrase, each word comes from a much bigger set than (alphanumeric + special characters), so it stands to reason that it'd be harder to brute-force. There are speech patterns, though, so it's likely that crackers would be able to reduce the search space somewhat by checking common phrases like "my first car".

But change to something like "my first grandma was a 1927 haircut" and you're likely to future-proof it significantly.