That works for counting colors. That WILL be number 15 when you work it. It's more a matter of how many rows have been worked--those are the v's. In this case row 15 is on the needle, and it will be your 15th purple row. I know exactly what you're talking about. It's really a matter of semantics, and there has been tons of discussions here and elsewhere about it.
In general, though, let's say you're supposed to knit 50 rows. You count 50 v's. The loops on your needle are for your bind off row.