Have to agree. I have a 'helper' most of the time, and even with 2 of us, 15 suites a week would be too much, and standards could not be maintained.
But thinking about it, if your in and out in 90 mins I suppose its possible.
It all comes down to what type of standard you work too and how you sell your service to the customer. Do you do all the suite, backs, under cushions etc, do you take time to explain potential outcome and possible problems, do you leave it dry to the touch? I doubt it.
When you enter someone's house you may not realise it but they will be watching and taking note of everything you do, if they see you rush in, give it the big splash then then take the money and dash off to the next customer I wouldn't expect to be called back the next year. Even with 2 people 90 mins would not be enough time to do a thorough job, even with 2 machines, which would be a complete mess to work with and laughable to think of. Having 2 people does not make that much difference i find - maybe half an hour less.