It seems unlikely that Darcy knows that she suffered that greatly from her dances with Mr Collins. And even if Darcy did know that Elizabeth regarded the dances as ones of mortification, surely it is nicer of him to not wish to suspend any pleasure of hers?

Though I think Elizabeth got a fair measure of pleasure from the ball despite all her disappointments:
Elizabeth listened with delight to the happy, though modest hopes which Jane entertained of Bingley's regard,...
It's lovely to see how Elizabeth forgets all her miseries when her sister is happy.