When the electric windows start to work slowly going up or down the window mechanism is starting to fail, to lubricate anything the door interior trim panel needs to be removed to inspect the window operation mechanism and window channels. Perhaps try lowering the window and spray silicon down the window channel. Always operate the electric windows when the engine is running (higher available voltage at the motors).
my car does that. and sometimes the front passenger window does the same thing... i think it's just slowing down from overuse. if that's possible... i tend to just leave it alone for a bit and then it works fine; or, keep pushing the button and eventually it goes down.