Throwing my two cents into this....having played slot tournaments and challenges in the past that required to win a certain multiplier to complete the task, it was always the BET AMOUNT times whatever multiplier.
So - if you spin $1 spins and win $15 - you complete.
If you buy a $100 bonus buy & win $30 - you DON'T complete the task - you would need to win $1,500 to get the credit for it.
The same "should" apply here but I'm not exactly sure if that is how it was intended or not.
This also means that if you spin a $1 base game hit, and land the bonus and win $15, you complete the task even though you got 15 or 20 bonus spins - the base spin counts for the value of the bonus, thus completing the task.
@Debi @Tammy - Am I correct in that or no?