Earthing pin is taller. This is a way of keying the receptacle so a 10A or 15A load can plug into a 15A receptacle, but a 15A load (tall earth) cannot plug into a 10A receptacle.
North America does exactly the same with NEMA 5-15 and 5-20 and 6-15 and 6-20, just more obviously (which helps users understand why it won't fit).
And it's probably the same thing: it means the cabling behind the receptacle is either the thinner cable that saves money, or the thicker cable with higher current rating installed at extra cost. With a different size overcurrent device (breaker) for each to protect the wires.