This is implausible. There is no conceivable motive for people to support the hypothetical robot army; there is not a chance in hell that 1.5 million people would voluntarily build a robot army for a tyrant, who doesn't have the many trillions of dollars needed to pay them (since nobody has that much money)

For a start, I don't believe you. People have done comparable things for tyrants in the past (complete albeit probably inefficient dedication of the resources of the given tribe to the objectives of the tyrant---horseback archers and small moustaches spring to mind). But that isn't the primary problem here.

The primary problem would be with a country creating the army in the usual way that a country creates an army but that once owned this army would be much easier for an individual (or a few) to control. It makes it easier for such people to become tyrants and once they are to retain their power. This kind of thing (a general seizing control by use of his control of the military) is not unusual for humans. Killer robots make it somewhat easier. Controlling many humans is complicated and unreliable.