Especially for XBox360.
I was thinking about downloading RAAM's Shadow, for Gears of War 3. For games I know they reach the €20 mark sooner or later, usually later. When a full game is €20, €15 seems too much for just an expansion of a few hours of campaign for that same game. I'm not a big fan of DLC and I didn't check how prices vary through time for them, I think it's reasonable to expect it will hit the €5 mark at some point, which would be a fair price IMHO.
Am I being too optimistic?