But that in turn is less efficient than 0 desks for 15 people.

Thinking about it, why stop there? Negative desking is the future. A team of 15 could have -15 desks (or less, if they are high performers). Super efficient.

Is it?

Of course, neither of us nor the company really has hard knowledge of what is "more efficient", because despite being entirely driven by profit metrics and A/B testing there is still no real way to measure productivity for knowledge workers. And even if there was, employee misery wouldn't be part of the metric unless it measurably affected retention.

Works if people aren’t coming in every day. We have set days where certain teams come in. You’ll be sitting next to the people you work with and the company doesn’t need as many desks

but they cram them in like factory chickens