FR's charges are now far above industry average but then again their fares are lower. FR want passengers to travel with hand luggage only and check in online, it will cut down handling costs and reduce the time spent on the ground. However, obviously not even MOL believes the day will ever arrive where 100% of passengers will do this, so in the mean time they will make a nice amount of money from it.
It is working though, the amount of online check-in pax has climbed so much that some routes are seeing way over 50% of pax avoiding check-in.
I think it's fair to say to Ryanair that fuel costs have dramatically increased, and so therefore those 15KGs obviously cost more to transport now than say this time last year, therefore you need to pay for it.
I don't think the charges can really go much higher though before it begins to have a negative impact on demand. Time will tell.