Wait, you want to do all those continents in 15 days? Are you insane? The adventure would be all the traveling you'll need to do in such a short span of time. If you are set on that route, get yourself a round-the-world ticket and hit Sydney, Buenos Aires, Rio, a Caribbean hot spot like Jamaica or Barbados before hopping back to Europe. I'd actually do the Middle East of Africa (Cairo? Dubai?) first before flying down to Oz. All that said, unless I'm misreading your question, I think you'd be much wiser to focus on a region like Southeast Asia and Australia or South America and make the most of your time there.