How can I tell the difference between the Deva realm and the Buddha and bodhisattva realms? How can I tell the difference between joy bourne of karma that will expire and joy bourne of karma which has turned the irreversible wheel of the dharma?
Denizens of the heavenly planets enjoy more and live longer. They have made lots of good karma in their human form of life and became qualified to enjoy heavenly life. The joy of of Buddhas is eternal and unlimited. Buddhas enjoy their natural life that's found in enlightenment.

The best way to know this is by gaining experience from meditating.