PoS coming soon?
That should be coming sometime mid-2016 I think, so I'd expect it around June-July 
link please
http://stackoverflow.com/questions/33802343/when-will-ethereum-switch-to-proof-of-stake
Ok, according to this: http://ethereum.stackexchange.com/questions/874/what-is-the-set-number-of-ether-in-existence-during-pow-and-then-pos
it's Q4 2016.
Anyhew, a fresh video interview with Vlad Zamfir: https://www.youtube.com/watch?v=StMBdBfwn8c
Edit: This interview seems to suggest that you'll need much more than 1500 eth to mine PoS. He is suggesting as low as 100 validators.