It's 15kg per person, however many items. You get 10kg hand baggage. 25kg is enough for anyone on short haul flights.
the whole baggage thing is just one of Ryanairs scam's. It was 15kg, then 20kg becuase you were paying for it, and then 15kg again even if you pay for it. If you just have hand baggage, you still have to pay a supplement, but it gets you "priority boarding"
I fly Ryanair regularly, and have no real complaints as it is the airborne equivalent of National Express coaches.
I do worry about the marginal commend of the english language displayed by their flight deck and cabin crews !