Is 15 even linked to anywhere? Those that are hard to find are fine as they are I'd say, they're not really bothering anyone this way.

As for the rest, many are kind of dead indeed, but at the same time that means moving them wouldn't really change anything except their place on the forum index page. If people would be reviving threads all the time I'd consider moving them around, but right now I think there's not much reason to change things.