Well to compare temps, I put it at a 12-13 degree difference in equal "feeling." That's a little more than the heat index generally has it.
Ex: 100 in Phx feels like 88 in Gainesville. Heat index in FL due to humidity tends to add up to 10 degrees, not usually more than that.
The 115 AZ heat is worse for 3 reasons, though:
a - it stays hot all night....it was 98 at 11pm here the other night. There is no relief.
b - FL has nearly daily storms that are accompanied by cool breezes and cold rain. A reprieve. Daily.
c - The 115+ day after day with no clouds just makes everything hot as hell - every door handle, your car, the ground. Everything stays burning lava hot.
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Idk, here's a morbid take on it: people voluntarily enter saunas. They have to be forced into ovens.