Plenty of perfectly good thread titles are only one or two words (especially suggestions), and the 15 character minimum doesn’t really serve any purpose - just results in a lot of “New Boss Leak (15 characters omgomgomgomg)”.
Since we’ve already removed the character limit in posts (or set it to 3), it figures we should remove the one for post titles too. The first post in every thread will still need 20 characters, so it won’t be possible to accidentally create a thread or something.