Fahrenheit is the nicest temperature scale because its the only one where 69 degrees is survivable.

Anyway this leads me to the second point:

If my math is correct then about 15 million years after the big bang (z=106.7 (15.072 Myr)), the universe was nice.

That’s just facts tho:
69°F -> Not too hot, not to cold all you need is a light jacket. Perfectly survivable with no gear
69°C -> 12 degrees above the hottest recorded temperature on earth (56.7°C)
69K -> >200 degrees BELOW the freezing point of water (ALSO below the coldest recorded temperature on earth (183.95K))

Thus the other two aren’t nice.