I'm not sure about temp fluctuations when a woman is on BCP. I was on it for 9+ years, but I never charted or paid much attention then.
However, BCP itself is generally a combination of estrogen and progesterone. One form of BCP is only progesterone. Progesterone in the first part of your cycle will prevent you from ovulating altogether. Hence the effectiveness of BCP.
However, when you aren't on BCP, the first part of your cycle is dominated by estrogen, which is indicative of lower temps. After you ovulate, progesterone takes over in the event that the egg is fertilized because you need progesterone throughout your whole pregnancy to sustain the fetus.
So you will typically see a noticeable temp increase during the luteal phase, after ovulation, when your body is dominated by progesterone. After ovulation, most women with normal levels of progesterone will see their temps increase by at least 0.5 to 1.0 degree during the luteal phase. If a woman gets pregnant, the temp generally increases even more.
While you did just come off BCP, it's not unreasonable to assume that your body will ovulate right away. A lot of women do; some women don't.
I also wanted to add that you may not have seen a massive temp spike, but your temp steadily increases after CD 15. And the day after CD 15 saw a 0.4-degree jump. That's enough to assume ovulation. Yes, having more temps would help make more sense of your chart. However, I don't think you have anything to worry about. It looks like your body is normalizing quite nicely.