I go to a fairly “elite” private boarding school, and I applied this year to 19 schools. I was going to apply to twenty, but I just couldn’t emotionally finish my Harvey Mudd App at the last minute. If you’re prepared to apply to 24 schools and it doesn’t pose any fiscal hardship, go for it! I think honestly it’s person dependent, and you recycle a lot of essays anyway. After getting some admissions decisions (4), that have gone in my favor before RD, I somewhat regret applying to that many because there were some that I have 0 interest in attending (even if at the time I convinced myself I did). I think 15 schools should be perfectly fine/enough, but if you want to do the 8 ivies/stanford/mit/every other top 20 schools, I completely understand it. Once you get into one of your top choices you’ll wonder why you did it, but I think it can be worth it if you’re insecure about your app.