As you are aware Uncharted 3 Single Player is free for plus, now in EU its only 12gb I Know this doesn't include MP but U1 was 18gb? Goes to show that the 3D took up a huge chunk of unecessary space
I'm afraid you're wrong.
UC3 SP: 12GB
UC3 MP: 5GB
UC3 2D cutscenes: 13GB
UC3 3D cutscenes: 11GB
There are also various language downloads if you want a localized dub.
Hint: you need at least 3 of 4 downloads to play UC3 SP. 3D cutscenes are optional. MP download is compulsory.