You would see a ten minute match with careful strikes, rare be any tricks.
My duels with Urist never finish before 10 minutes anyway, just with the chance of permadeath I wouldn't intentionally die after hitting the 15 minutes mark.
If this condition were imposed I do think it would be a test of patience as cRPG is already, this is due to feints being high risk low reward here. I personally would stop chamber blocking even though I rarely miss, I would perhaps turn to backpedalling since it's by far the most effective duel tactic without little downside. Kicks would be used more carefully too, nobody would want to risk that stab coming in whilst kicking.
To be honest since I don't really play cRPG any more, I wouldn't be too worried about losing looms. I only play cRPG since the 22nd are here and thus only fight strat battles where my few looms aren't used anyway.