The datasheet says the resistor can handle 5x the three-watt rating for 5-seconds. Thats all we can know for certain because it has been tested. Anything after that is on you to test. If you are asking because it is a fun experiment, try it and let us know. If you are using it in a power supply for a medical device that will be operating in a child's bedroom unattended, well, you'll need to have some support from the manufacturer or a certification from a third party testing lab and a contract with the manufacturer that they will not make any changes to the raw materials or manufacturing process.
Don't burn down your own house or anyone else's house.