I have some of the 13.5mm white connectors from Ray Wu back in stock. I will have more next week.
These connectors are identifiable by the YL on the moulding.
I assume rightly or wrongly that the 15mm connectors can handle more amps and have larger connectors, and larger wires. Otherwise why sell them?? If my assumption is wrong then 13.5mm is way to go as they are smaller.