[overlords]

Something is wrong with that argument. Welfare + Taxation = Basic Income.

Already we have it, by definition - it's an equation.

So some part of your calculation is wrong.

Likely you're over-inflating the amount paid out (it's not going to by 15/hr person) and undercounting payments (maybe disabilty/housing/local programs).

UBI given at equivalent levels to today's welfare would be strictly cheaper because of the reduced adminstration cost.

(this though is different from the question of whether payments should be higher and paid by increased taxation.

And off-topic, but taxation doesn't need to be increased - it can be payed by helicopter money, but actually not cause inflation, because of geographic mobility deflating that aspect of the economy).