FCC Part 15 regulates low power, unlicensed devices that could cause interference to the Amateur Radio Service and vice versa.
FCC EMC Testing is done at certified labs such as UL. Prior to investing the time and money to achieve certificiation, customers will setup and take measurements with mobile equipment to get an idea how their product performs against the emissions levels described in the standard.
FCC Part 15 covers an assortment of electronic equipment that generates RF energy whether it's intentional, unintentional or incidental. Amateurs will need to consider Part 15 as it relates to digital devices, computers, low-powered, unlicensed transmitters, electrical devices and any other "generic" device that might generate RF in the normal course of its operation.