So if someone had lot of bitcoins by accepting paypal on 15% Preev rates would they profit of that?
Yes, you could make money off of currency exchange. Usually (and I speak from experience both on and off of this site), when one converts bitcoin to paypal, he'll get more money than the USD worth of his BTC. It's usually not a huge amount, maybe a 5-10% gain. Regardless, this is a profit and it can be used to one's advantage. If you have the option to do this, it could be a solid way to make money. You'd need to find some place to convert your paypal/fiat to bitcoin at 1:1, but after that you should be good to go.