When is ovulation likely to occur?

Patient's question:

I have a question. My period has been around 15 days. There is transparent liquid discharge, but the temperature is not high. By the 20th day, my basal body temperature has risen. What does this mean? Was it ovulation on the 15th day or the 20th day? I don't know. Please tell me when it's most likely to get pregnant after we get together.
First follow-up question: After the 20th day until around the 28th day, the temperature only dropped after a few days, or it didn't drop until after the period. Which is it?

Doctor's answer:

Hello: Ovulation can be measured by the following methods
Basal body temperature measurement. That is: the temperature measured after the body has been asleep for a relatively long time (usually in the morning) and before any activity or speaking, is the basal body temperature. Under normal circumstances, the basal body temperature of women of childbearing age is lower in the first half of the menstrual period and even lower during ovulation. It can suddenly or slowly rise by 0.3—0.6℃ within 24 hours to a few days after ovulation.
Your situation is that ovulation occurred 20 days ago, and your ovulation period temperature is the lowest