This quiz was inspired by Jerry928's comment on www.jetpunk.com/quizzes/most-populous-countries-2050-quiz.php. Also, the world population would be 8.757 billion. The next country in the list would be South Vietnam with 85 million. In general, the projections are higher than the real populations in 2015.
The thing is I couldn't find any actual projections for 2015 from 50 years ago so I made some very simple predictions, ignoring (most importantly) the decline in population growth in industrializing and developed countries. The projections made by experts are probably more accurate than mine.