Core voltage is going to be in the ballpark of 1V, and given the stated power consumption is 15kw that means a minimum of 15kA. So, it is indeed a lot but the math checks out.
how much of that power actually reaches the chip though? (it's hilarious that this is one chip)? this thing is mostly a water pump - I just can't - everything about it is just wild
Most of it. The water pump and other stuff consumes probably less than 500W total. There's some efficiency loss in the actual power converters, but they're likely designed to be >95% efficient (probably >98%), otherwise cooling them would be a nightmare.