Q: Does it mean that I am pregnant if my bbt temperature goes up in a triphasic curve on 15 DPO?
A: The BBT (Basal Body Temperature) curve is used to look retrospectively at the day you ovulated.
Typically, the temperature rises within 1-2 days after ovulation and stays elevated until the menstrual period arrives. This is called a 'biphasic curve.'
A 'triphasic curve' is a curve where the temperature rises again, often within 7-10 days after ovulation. There is no scientific proof that a triphasic curve indicates reliably enough that there is implantation and pregnancy.
The best way to diagnose a pregnancy is to miss your period and see the BBT elevated for more than 14-15 days after ovulation. If the BBT is elevated for more than 15+ days without a period, there is good probability that you are pregnant.
So in your case as you are now 15 DPO without a period chances are that a positive pregnancy test at that time will usually confirm the pregnancy.