You lost 15 usd, so it is scam? It doesn't make sense, many people have won more than yours. Although your logic is not right, bitcasino.io reputation is quite bad, many ppl accused they are scam.
Thats a wrong perception. You win or lose in casino and in case of losing you cannot declare it to be a Scam. Win or lose is even even is Gambling and i dont think one can always win in gamble.
A few of my friends gamble at BitCasino and Win mostly, so its not a scam at all.