Cleaning and turning around keys-in to keys-out in 15 minutes probably rarely happens at Hertz in what I've witnessed (I've rented >100 times from them). But that said, most cars probably will come back at least 50% charged, so it is only 15 minutes to charge (while cleaning in parallel).

And perhaps if you're a customer picking out Model 3 cars on the lot and you pick one not fully charged.. you could decide to wait it out or just drive.