It ends up only being a $5 discount without the need to bother with game keys anymore (although there were ways to avoid the game keys too). Prior to this, it was $20 to buy the Battle Chest, and that came with 30 "free" days of gametime. Now, it's only $15, but you don't get those "free" days anymore. Overall, the discount is nice for those who wish to save $20-$25 when starting up a fresh team of five, but now we'll never see those $5-$10 sales anymore.

Also, word on the internet is that if you have unused Battle Chest game keys lying around that Blizzard will give you some game time for them.