This completely ignores Friedman's concept of the velocity of money (MV = PY). If that $15k is being saved by someone versus immediately spent, that has a different effect. A transfer isn’t neutral if the two parties have different propensities to consume (marginal propensity to consume). Similarly how quickly and what the money is being spent on will have an effect. Most money (M2) is not created directly by the treasury but rather indirectly from large banks lending against fractional deposits. This is money created on the balance sheets of banks but has real effect on the economy.