There is a hard cap on the amount they need and that's 20 btc. (not per user, it is a site-wide limit) So they are spending 3btc every year to pay investors.
Yeah that kind of cap makes it more feasible to actually be able to sustain that 15% return for longer period of time.
Do you think they can't afford to pay it?
I don't now, but I am not willing to risk my bitcoin in order to find out.
