^ Yep. 3 million sales at $15.
Or to put it another way, 45 million dollars for 3 maps worth of work (maybe 500 man hours if you're really pushing it?). Something like a 450,000% profit margin (and of course, those who actually did the monkey work will see nothing of that).
My question is who is doing the work now? Pretty much everyone left IW
Doesn't take an army of developers to put together a few levels - if you already have the assets, all you need are a couple of people who can work their way around editor.
If you're porting maps from the previous game, I'd anticipate it's almost as little work as dragging the map file across, then including any additional assets needed to make it work.