I have bought an industrial quality 15A extension cable (from
these guys) with 2.5sqmm cable so that when I have access to a good 15A socket I can use that, and other wise use the Amphibian adapter and run with less loss. It also means that I can carry just one extension cord for charging on the road. EEC also can supply cables with 4 sqmm cable but only with screw-lock industrial connectors since the larger cable does not fit in normal heavy-duty plugs and sockets. Any of these will quite happily run 15A continuously. I calculated about 50W dissipation of heat for the 20m cable that I have. That will barely make it warm.
For the unknown quality power points, one option if you are desperate is to plug in the 10A tail and then set the car to only draw 8A. Sure you will only get about 1.7kW charge, but at least you will not set fire to the house. If you are really unsure, then start at 6A and then increase if nothing is getting hot.