By all accounts, Tesla neither have particularly stringent QA nor a premium car level of interior.
By which accounts? I've honestly never heard anyone complaining about QA or "Not Premium Enough"
For example, Top Speed suggests that all other manufacturers are still playing catch-up. That it'd be nice if the seats had been updated a bit, but otherwise things are great.
http://www.topspeed.com/cars/tesla/2017-tesla-model-s-ar1729...
Next, the QA on a premium car has to me more stringent, simply because the expectations are higher.
So I can't imagine luxury car not taking more time to make than a budget car.