@arn From my point of view and experience, this problem is a combination of your Java script, ads, and trackers! There is a considerable difference in the default "Accept all" cookies, compared to customised settings. And that depends what the user selected in the pop up! Moreover, as a contributor, even if I accept all trackers, there is no battery drain. So then, that leaves the ads.
As anonymous or logged in non-contributor, I can reproduce battery drain with or without debug! It does not make a difference!
Revisit your ads handling AS ANONYMOUS USER, not logged in, and you shall find your answers to the performance of this site. Then, compare your handling of ads as logged in user no contributor, to that of logged in user but contributor.
I mean I am fine to contribute $25, you guys have to make money. BUT, this forum is not healthy, it is not right to burn user's cpu cycles and battery as if you were SETI@Home.
Edit: I don't believe this is a safari 15 bug, I have had this issue from a long time, and I thought it was my iPhone X weak battery... that was draining fast. But no, after became contributor iPhone X battery does not discharge fast!