Amps and speakers are rarely as fussy as theorists would like you to believe. If it sounds OK it probably is OK. Try it quietly. If it starts to distort, and if turning down does not immediately cure it, end the experiment.

Alternatively, on the figures you give, put a 2 ohm 10 watt resistor in series with the speaker. It won't go as loud, but that is not your concern.

Bear in mind, if the experiment is a disaster, what do you lose? You have to buy new speakers, which you were going to do anyway.