Hi
Sofronii
My English is not my first language but i will do my best...The forum here have a full of informations i spend almost two years to read posts on it.
About the 15 % of body it's seem to me too much. (if you search on this forums you will see probably some posts by a member named
dougfitz and he explain many things about this). Me I used 10% of body weight...and a kitchen scale....i weight everything my glasses my watch...yeah I'm crazy.
But i think 10% is a guide line, I explain myself: if the person weight 250 lbs he does not need 5 t-shirts and 8 pairs of socks. So i think it's good to compare items between with an excel sheet and then i realize how all the stuff you want to bring weight together (and don't forget the bag itself). But if you take all your stuff including the clothings you are wearing your shoes/boots and you weigh it and is less than 15 % it's can be ok. (i think it's call skin out weight)
For the size of backpack: it's good question
, an advice I read here is to bring all your stuff at the store when you are ready to buy your backpack and you will see how big you need. don't forget space for the food you will buy on the way. I said it to you because the type of raining solution you choose and if you bring a sleeping bag affect the size of the bag.
By the way my bag is a Osprey Talon 44 (I'm not working for Osprey), i did the camino in July-August and i bring a sleeping bag. Will i bring the same bag for next Camino? Yes i Will. And the weight was about 7.5 kg.
I hope my English is clear and you will understand what i want to say.