Well the more the better right? You can certainly overdo R.C.s, where you do them so often you don't think of them anymore and they just appear all the time in dreams but you never notice them- but every 15 mins is hardly enough to make them blend in with you dreams. I started at 9:00am this morning and it is now 10:15pm. I have not missed one this whole day, even when there was no clock. I did one in the shower just before I got out because it felt right and when I looked at my phone it happened at the correct time.