Most buyouts happen when the player gives up most of his contract so he can play somewhere else, usually with the belief that his next contract will be bigger than the one that was bought out. A player slated to make $5 million takes a $1 million buyout and then signs for a MLE somewhere else for $5.8. That kind of thing.
The Hawks buyout of Carmelo a few years ago was definitely unusual, and the Hawks were tanking. Now that tanking doesn't work, I don't see why a team would pay the majority of a contract to have a player not play. It is cash out the door, and it counts against the team's cap. That team will also have to pay the replacement.
I imagine if Iquodala asked Memphis to buy his contract out for $2 million, they might listen. I suspect that if he asks for $15 million, they will tell him to show up at camp ready to play.