Any ATC clearance cancels the previous clearance.
What Zooker says is correct, however, I would still expect you to slow to 220kt at FL150 unless you were explicitly given another instruction regarding speed. By the book the controller should have reiterated the speed restriction when you were cleared to FL80, but being busy and having it in his/her head that they've just instructed you to fly 220kt, it wouldn't be something they would necessarily think to say again.