Most 'pretenders' I've come across over they years have outed themselves by cheating in the most idiotic ways on screening questions and failed to answer the most trivial coding questions because they've been so bad that they didn't understand even the level that was expected.

So I'm inclined to think your 15 minute intuition is nearly enough - the worst people reveal themselves very quickly. And so does the best people. Where a little bit more time might be needed is sometimes in the middle, but it's rare for more conversation to change the initial judgement.

Over nearly 30 years, there have been borderline cases where we might have overpaid someone, and a couple I'd have preferred not to have hired, but who still could deliver, but I don't think we've ended up with anyone who were bad enough to justify these kinds of extensive hiring processes.

I tend to see these complex hiring processes more as tests to determine which candidates are willing to jump through hoops and prove their eagerness and loyalty. E.g. when a FAANG sent me a reading list.... I declined, pointing out that if I needed to study for their interviews they weren't testing my skills, but how desperate I was to work for the. Their recruiters called me back a couple of times to try to convince me again.

I can understand them doing so, because they can, and getting people to who will see it as an achievement to get past these barriers might be worth it to them, but to me it just felt like I didn't want to work in an environment where people were so eager work there that they'd put up with that.