Christine that'd make it a 10 or 11 day LP which is more accurate. Do you use OPKs? Are you sure you ovulated 15 days ago?
Are your cycles always 28 days? Since coming off the pill I've had a 31 day, a 28 day and a 34 day cycle. Going by ovulation pains over the last few months and this month, using OPKs, I am on a 32 day cycle this time.
If you use OPKs to find out when you ovulate, then you have a period X-number of days later, this is your Luteal Phase which doesn't really change much each month (if at all) so if you ovulated on the 1st of the month, and your period arrived on the 15th, you have a 14 day LP.
What determines the length of your cycle is not what happens after ovulation, but it's the bit before - the follicular phase. So on the month I had a 28 day cycle, this phase was shorter and month I had the 34 day cycle, it was 6 days longer. My LP on both months was 14 days.
This is the reason I now use OPKs - I couldn't tell when I would ovulate as it could have been earlier or later than the previous month.
TTC is a massive thing to get your head round and it all does become quite confusing x