TOS regarding minigames which feature no losses

I’m not entirely sure if this is the right category for this question (please correct me if it’s not) but I’ll assume it is and go forward.

A friend of mine is working on a limited / case clicked type game. I’m working on something similar but with a spin of donations and wagering.

AFAIK (gone through the TOS) my game idea is fine, but my main question is if gameplay which features gambling type content (ie. Mines or Limbo) is allowed, given there is no way for you to change the amount you wager, and you can only win or break even. His idea was to make it playable once every 15 minutes, which seems fine to me. Is this allowed?