Really? As i remember it was around 25 dollars. One part is buy in and the second (smaller) part was sent to some account (for additional prize in final). Anyway, 15 dollars looks like good enough for me 
Will try to join next series
That was the BTC tournament on SWC, in this series we've only been doing the entry and it's FIAT based on Betnomi with a 15$ entry. We haven't run a side pool at all here for lottery or anything like that. I've preferred it this way. I can't even remember what it was at the time but I think it was still around 15 USD at that time depending on price. Will try to join next series