I have just bought a 2022 MG ZS ev (essence) and have used the granny charger on my ordinary house power socket (10a?). I have been looking for advice on using an extension cable with the granny charger if I go somewhere where the lead won't reach. EV forums have said never use an extension lead, others anyone will do, others make sure its uncoiled, check it for getting warm and make sure it is at least 2.5mm squared core wire. So all the usual outlets Bunnnings, Mitre 10 don't go up to 2.5mm, except one at Toolshed.co.nz. This is 10metres 15amp heavy duty with 2.5mm Squared wire. $69.90. Sorry can't do a link as i'm new.
I don't know about the MG granny charger.
My granny box has the option to set the charging current. I leave it on the default 8A.
In any less than ideal situation (like introducing an extension cord) I'd dial that down further.