Even when getting 15 free spins you have to make a deposit to claim it there is no way to have fun 
Any casino security system is unable to detect greedy people. If the bonus can be withdrawn without the requirement, then people will create as many accounts as possible just to claim bonuses, don't really want to enjoy gambling.
At least it can use other ways to increase wager requirements for example FJ made the same promotion but no one managed to make a withdrawal
This is better than having to deposit first but I understand every casino has its own offer. maybe if next time Riobet offers something interesting I will try.