Here's a little trick to remember which direction to turn the spanner when removing pedals:<br />With the spanner at the 12 o'clock position, turn it towards the rear tyre to loosen the pedal. This works for both the left and right pedal.<br /><br />The left pedal has a left-hand thread, and it's thread is opposite of the normal right-hand threads found everywhere else on the bike.<br /><br />I've found that a 15mm spanner is sometimes just too big, and can slip when you put pressure on it. I suggest you wrap a piece of cloth around your hand in case the spanner slips. You do need to apply a fair amount of pressure to loosen pedals.