I think you've constructed your utility wrong in this instance. Without losing track of scope, we have 3^^^3 motes of dust in 3^^^3 eyes. And yes, that outweighs 50 years of torture, if and only if people have zero tolerance. But people don't break down into sobbing messes at the (literally at least) slightest provocation. There is a small threshold of badness that can happen to someone without them caring, and as long as all 3^^^3 of them only get epsilon below that, the total suffering for all 3^^^3 of them summed is exactly 0. We have 3^^^3 people, and 3^^^3 motes of dust, but also 3^^^3 separate emotional shock absorbers that take that speck of dust without flinching.

It is non-linear. If you keep adding dust, eventually it starts breaking people's shock absorbers. And once those 3^^^3 people start experiencing nonzero suffering, it would quickly add up to more than fifty man-years of torture. Then the equation stops favoring dust motes. And here I hope I have some other recourse, because "If you ever find yourself thinking that torture is the right thing to do," is one of my warnings. I hope I can come out clever enough to take a third option where nobody gets tortured.