I'm not sure this is going to actually help anything. As users who can't reach the minimum character count have demonstrated, they'd rather find odd ways of avoiding the minimum limit that require more effort than just typing some extra text that supplements their answer.
Which of these would you rather see?
If people really don't want to think up a simple 15 characters, there's nothing that's going to stop them. Most users who don't know about the null byte characters and the HTML comments just fill the space with random, meaningless characters such as
sjfgshjfs to bypass the limit, or use other styles (headers, bold, italics) to make the text stand out when it doesn't need to stand out.
Personally, I'd much rather see the first one. It may be a character bypass, but at least it doesn't look stupid in general when you look at it. Ultimately answers which use these are probably not real answers anyways* and will end up deleted or get fixed by someone else.
* Unless you're on Meta.