Ryanair are generally very strict, both on size and (especially) on weight. Their carry-on limit of 10 kg (22 lbs) is in fact on the generous side for Europe; a lot of airlines limit carry-ons to between 5 and 8 kg. Their checked baggage limit of 15 kg is 5 kg below the standard limit applied by other airlines.

They don't weigh every bag, but they do a lot more weighing than any other airline I know. If your carry-on is more than 10 kg you have to check it or transfer the excess into checked baggage. If your checked baggage is more than 15 kg they send you away to pay for the excess, and their per-kilo rates are the highest of any airline in Europe. From what I've heard they've even now become wise to the usual tricks of putting small heavy items in one's pockets - I've heard of people being asked to take off their coats and put them on the scales!

BTW, you say you are flying from Munich to Oslo. Where are you REALLY flying from and to? Ryanair claim to fly to Oslo but they don't, they fly to Sandefjord. Munich they don't even CLAIM to fly to - but I guess you could be flying from Salzburg which must be about the same distance from Munich as Sandefjord is from Oslo.