It depends, really. If we're removing both 10 and 25-man raids, then yes, I'd like to see 15-mans... But, if Blizzard decided they wanted to keep 10-mans, then I'd say change 25-mans to 20 instead, that way, instead of a 2.5:1 ratio, it would be a 2:1 ratio, which would be much easier to balance around.