If its not dead ball (and I understand Harv's argument that is was the same as Lang's last week) then either you decline and take the sack for minus 7 and the down OR you take the penalty, the down doesn't move and instead of loss of 7 its loss of fifteen.
I gotta be honest, I would rather take the down away on a sack than accept the penalty and replay the down. But 15 PLUS the sack and down would be ideal.