That is the optimal amount of sleep.
In fact, Perelman was reported to sleep approximately 14-16 hours a day when he was working on Poincare’s conjecture. Wiles slept even more than that 16-18 hours a day.
Personally though I generally keep it at 12 hours since I’m a wagecuck, though on the weekends I generally go up till 16. Not really much point going past that though, as the benefits of sleeping more than that much aren’t worth the proportion of time awake you sacrifice.