He was pretty terrible after his last nerf. Riot has acknowledged that his kit can screw a lot of champions when it is too strong, and they are working on a rework, but those aren't good excuses to just leave something extremely weak indefinitely. If we can give a buff to a weak champion that won't make them extremely oppressive to other champions, then we should (and until I see evidence, I'm not going to believe that 15 damage is the difference between weak and obnoxiously oppressive). Keeping a champion weak because we're too scared of giving small buffs is how we get stupid Olaf and Urgot situations.
It's not that big a buff. He's still not going to be great. He'll just be less bad. That's a not terrible state for him to wait for a rework in.