Hi Rach
15mm doesn't seem too small when you still have 3 days to go. TBH I don't know about the lining - I was never told what mine was. How much have they dropped your dose this time? Going from over stimming to 1 follie seems a bit unusual - although I've only done ivf, so I'm guessing iui is different - they probably don't want you to release 12 eggs at once! Are you able to contact your clinic to see if they can shed some light on what is the normal range? Sorry I can't be more helpful - Good luck!