FF may have a hard time picking up your O day, your temps arnt high enough yet to tell if that was O day, the dip at cd15, they would have to get up above the other temps and stay up there for there to be confirmed ovulation. At this stage even with another high temp ff wont peg cd15 as O day, ff may need additional high temps than the normal 3, it may not be ovulation at all, so I would keep up the bd till you get some crosshairs on there.