Your parents are concerned about your safety net.
The vast majority of people with the same dream as yours don’t make it in LA, just as most of the kids your age who plan on being pro athletes don’t make it to the pros.
So your parents are concerned about your backup plan.
You say you want to be a celebrity. OK, fine. You want to be famous. For what??? What do you bring to the table that justifies the fame you hope to achieve? What is it you hope to do that will justify the fame and fortune that you’re hoping for? What makes your dream more likely to be achievable than every one of the other 200,000 kids your age who have the exact same dream???
College isn’t for everyone. But I think that your parents are concerned that your plans appear to be “I’ll be rich and famous.” That’s kind of like saying “my plan is to win LOTTO.” As nice as it would be, I think your parents are concerned that the odds are very strongly against your plans turning out.
So let’s say that you DO make it big, but not until you’re 30, or 40 years old. What’s the backup plan for the years in between now and then?
I think that, if you could come up with a cogent argument for something along these lines, then you might find that your parents would be willing to listen to it.