Gday Tom-Tom welcome to CS.
my company CosmoreX Coffee is an equipment importer with many years experience so if you will permit I would like to addess some you your points.
These days most machines have internally situated pumps. It is much much neater and easier for installation. There is no advantage to having an external pump, except if you believe that by freeing up the space inside the body of the machine, the manufacturer might use it to fit a larger boiler. *Would a larger boiler be advantageous? Not really as most commercial machines are designed to do a job so are already equipped with a boiler of a particular size to do that job.
I doubt you will find any readily available single group commercial machine that runs on 15 amps. At that size, they are 10 amp machines.
You will find plenty of "kick" in a commercial 1 group machine with an internal pump and running from 10 amps.
Are you looking for home or for a business. What type of business, office or cafe etc.
In any case as stated above we are equipment importers and can probably help with one of our Diadema machines. I will be happy to answer any of your questions off site.
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