Why/How is it that many of my opponent's game time totally off but mine is accurate. In 15 min: 10 sec game there were 30 moves made and my opponent had 14min and 54 secs left at game's conclusion (I lost with 1 min or so left on MY timer?????????) This situation occurs more times than not. Why???
why is my opponents time inaccurate?

midniterain, the time control of 15 min : 10 seconds means that each player has 15 minutes of time at the beginning, and that after each move, 10 seconds are added to your time. So, as mijus has already said, if a players plays fast enough to consume only about 10 seconds per move, his time will stay about the same during the whole game.
Why/How is it that many of my opponent's game time totally off but mine is accurate. In 15 min: 10 sec game there were 30 moves made and my opponent had 14min and 54 secs left at game's conclusion (I lost with 1 min or so left on MY timer?????????) This situation occurs more times than not. Why???