Actually, I think you are confused on the differences between the 15 and 30 amp connectors. According to this page:
http://www.powerwerx.com/anderson-po...owerpole-sets/
The 15, 30, and 45 amp connectors share the same housing, the only difference is in the contact.
The reason that FIRST specifies 30 amp connectors is probably because the battery is fused at 20 amps. It would be poor design to use a connector rated for less than the fuse on the circuit.
I hope this helps.