I have an 8015, and the truth is, I don't notice that it gets too hot. Less than my previous Denon Series 4, which also didn't get too hot with its 7 channels in use.
Now, just in case, I added external fans, which work at a minimum and according to the same device do not exceed 35 ° C.
I added an external stage for the front trio, but before that, and with all 11 channels running with a usual volume around 70/98, I never felt too hot.
I doubted a lot whether or not I should buy the fans, they did not seem very necessary in my case.
Finally guided by the recommendations, I decided to control the temperature and protect the electronics to extend its useful life as much as possible, especially with a view to summer, it is too hot here ...