My Guten 70litre needs 15amps as well. Down here you can get 15 amp domestic sockets, slightly different plug on the 15 amp side so you can't fit it in a normal socket. You can fit the normal plugs in the 15 amp socket. Luckily the brew room ( laundry ) had a dedicated circuit with the correct cable rating I needed and all I had to do was fit the special socket.
If I was back in the UK I'd be thinking of a supply cable rated high enough in a way like the cooker circuit or the circuit to an electric shower and then either fit the Caravan style socket and matching plug rated for the higher current or wired directly in as per a cooker. With an RCD.
The big vessel does mean you can do big beers easily and obviously more than double batches, with two 35 litre systems you will be doing twice the work and cleaning and find that efficiency goes down with high grain bills.