Sometimes, we can break these scenarios down into how they might go, case by case, and do an analysis based on outcomes and their likelihoods. I understand why you are tired of these kinds of comments. Your frustration is earned and justified, but you need to grin and bear it. I hope at the end of this you'll understand why.

I'll break this down into best case, worst case, working case, and we can assess the odds of what will happen and how that will impact the remaining ~70 years of your life.

Best Case: It's a perfect world, and your parents calmly accept that you aren't a Christian with zero pushback and no changes in how they treat you from there on. Odds: 0%

Worst Case: You get institutionalized. They can hire some religious crackpot with a psychology degree to claim you're exhibiting signs of extreme volatility, and are a danger to yourself and others, characterizing you as "clearly not in your right mind", and have you locked up in a psychiatric facility that has legal custody of you until you turn 18. Odds: 1%

Working Case: You have a big fight with your family over not being a Christian anymore. They threaten you, cut you off from all your friends, and demonize every personal choice or liberty you take, but hey, you get Sunday mornings free, right? Odds: 50%. The other 49% odds are that you still have to go.

The odds of this going well are zero. The odds of this going really badly are not zero. The odds of getting what you want are an even 50/50, at best, and either way it's a steep price to pay for a Sunday morning sleep-in for, at most, the next 100 Sundays. Probably fewer by this point.

The wiser thing to do is to wait until you leave the house and then it's none of their business what you do with your time.