I agree, but to my knowledge it's fully legal in most areas. I'm thankful I caught them putting my office on the same circuit and fixed it. One of my printers alone draws 13 amps while printing. I just wish I would've looked into the rest of the house when I found the office wiring.
If you had a known 13A load, why didn't you have a dedicated 15A branch circuit installed for it? Its uncommon but not prohibited in residential construction.