I think 5% + Husbandry would be better so that they won’t be generic in Castle age. It is basically free husbandry during Castle age.
5%/15%/15% in Feudal/Castle/Imperial can also work but that will be a bit OP.
My biggest complain about this bonus however is Camel and CA units getting benefit from this bonus is a total waste. The biggest example of bad bonus on a wrong civ imo. (Only for Camel and CA)