The EU standard baggage allowance for checked baggage is 11Kgs Domestic, 13kgs European and 15Kgs International. The 10kgs hand baggage is included in the standard passenger weight (mass).
Subpart J refers.
As Ryanair operates within Europe, primarily, 15kgs baggage allowance is 2kgs more than the prescribed figure for weight and balance.
If Jet2 or any other company allow 22kgs I presume their weight and balance system accounts for this.