I have interviewed a lot of PhD applicants and trained a number of PhD students. We care absolutely zero about any courses/course credits from high school, and close to zero about research experience during the high school years. We usually ignore anything in a student’s application that happened in high school, and we tell our own undergrad students not to list any high school activities in their c.v.s.
I cannot imagine any realistic scenario where the high school research experience would be the tipping point in the evaluation of a PhD application. For our PhD program (biomedical in a medical school), the high school research accomplishments would need to be truly exceptional to have any impact, e.g. as reflected in first authorship on a Cell paper (for perspective, something most PhD students don’t manage to achieve).