Hi, I just flew with Ryanair (to Seville, weird coincidence Rusty); the 15kg is a good size bag, but not a ramjammed bag with three people's things in it. At Stansted they didn't give a toss that our bag was overweight, but at Seville they did. As someone else said, you can't spread your allowance over two bags, each bag must be under 15kg. We had a lighter holdall and we had to repack at the check-in desk and queue again, so we were the very last people to board the plane. They do this to make you feel pressurised into paying the excess, which would have been 100 Euros for us!
On the way to our holiday, with all the airport stress I was "why do we do this to ourselves, it's not worth it"...then on holiday, I was "This is so great and totally worth it" and then at the airport coming back I was all "not worth it" again. Add to this the eco-guilt of flying short-haul and I'm thinking hols in England/France by train in future. (We have to fly long haul once a year or dd wouldn't see her dgps).
Better that you know these rules in advance and pack accordingly, saving hassle and expense at the airport...
OH, and don't forget to put nappies in your carry-on luggage!! Yes, I actually did this, then dh thought it would be a good idea to buy swim nappies at the airport instead. Swim nappies don't absorb water...so it was a lap full of pee for dh, wet clothes for dd and a session in the toilet trying to stuff the swim nappy with toilet paper and fashion trousers out of dh's underpants for dd before I finally had the genius idea of asking another parent on the plane for a nappy.
Sorry for long post and thread hijack, but thought you might like some light relief from your packing worries!