Melinda,

Not sure if this helps but Fertility Friend rates BD based on 3 days before, the day of ovulation and the day after. I don't think two days after is going to work (although you never know). If you have DTD the day before (mmm CD 15 from what you said), the day of (CD16) and the day after (CD17) you should be right.

This will also be my first month using OPK's but not starting until Sunday or Monday.

Good luck and I hope the finds the egg!