Either size will be OK on your Minor but best to have all the same size of course! As Woody says, the larger 155 size is less expensive so they are the choice of many. The Nankang 155/80/14 suits the Minor well and is a good buy at present. Shop around and they can be bought very cheaply.
145/14 was the factory recommendation for radial ply tyres on the Minor but a great many owners choose to fit 155 section instead and have done for the last 40years to my knowledge. Has ANYONE on the forum experienced any problem from doing so?? I certainly haven't myself.