Can I plug a 15A snow thrower into a 15A receptacle?
Unless it came with a 20A plug (pictured below), it's designed to plug into a 15A receptacle.



The 20A plug has one blade twisted 90 degrees to prevent it from being plugged into a 15A receptacle. The corresponding 20A receptacle has a slot shaped to accept a standard 15A plug or a 20A plug:



This assumes that the plug on the snowthrower is factory installed and that someone didn't replace it with a 15A plug. If the motor really does draw 15A continuously, then it probably shouldn't be used on a 15A circuit as the continuous draw of the circuit should be less than 80% of the circuit capacity (12A for a 15A circuit).

Additionally, this assumes that the manufacturer put the right plug on the device. If it was purchased from a major manufacturer (and designed for use in this country) it should be fine, if it's from an off-brand and not UL listed, then it's less certain.