Ryanair Check in Baggage

Hey. I'm hoping someone may be able to help me. I've booked a flight from Dublin to Edinburgh for the 2nd week in September. When i made my initial booking i only wanted to check in 1 bag. But since i'm moving to Edinburgh to start college, i decided that i wanted to bring a second bag with me. So i adjusted my booking a few days later and added a 2nd check in bag. I was only charged an additional €10 for this bag, if i had added the bag on the initial booking it would have been €20. I was slightly worried my bag may not be accepted at the bag drop because of insufficient payment. I have also been looking at ryanairs check in baggage allowance. It said that a max of 3 bags could be checked in, but they could only have the max combined weight of 15kg. Since i have paid to check in 2 bags does this mean that each bag will have its own weight allowance of 15kg, or will it have to be 15kg between the two bags. I don't know if i'm reading ryanairs policies correctly and i'm getting myself all confused.
Any advice will be greatly appreciated.