Welcome to Fluther (if I hadn’t said that already).
As a 15-year-old, you’re starting to mature and wanting to pick your own path through life, which is completely normal, to be expected and applauded – at least to a point. (We’ll get back to that.) On the other hand, you’ll always be your parents’ – and probably especially your mom’s – “baby”, and many times parents aren’t so willing to let their kids grow up, and sometimes even less willing to let them choose their own path. Unfortunately, while that’s not what I would consider “normal”, it is fairly common and not completely unexpected.
Now, of course, there’s a new dimension to the family organization, or at least new to the dynamic you have described regarding your religious instruction: your aunt, apparently. A lot of “church ladies” do like to extend their sway over other family members in much the same way that you have described. (Maybe a lot of men do the primary moving here, too, but it seems less common, at least in my limited experience.) Or it could just be that your mom has always wanted you to be more aligned with church teachings, and your aunt and uncle are convenient allies. Who knows?
In any case, you’re not in favor of the added instruction, and that’s not uncommon, either, especially if your history is anything such as what @Seek has vividly described of much of her own experience.
One of the lessons to learn about maturity is not just about being independent and making your own decisions about things, but also – and this is a much harder part for too many kids these days – being able to intellectually defend your choices. That is, making calm, solid, reasoned and well put arguments (quietly, for the most part; I’m not talking about yelling and screaming matches) to support your case. It’s also frequently about negotiation and (frequently) compromise.
And that’s where we circle around back to the point we left earlier: It may be that your mom has been convinced by others in the family that, for example, your attention to video games (or whatever) is unhealthy, unsafe, and a distraction from growing up and bettering yourself. No one is going to approve of choices that you make which they believe to be unhealthy, unwise, dangerous, illegal, etc. And if you’re going to be perfectly honest – and you should be, at least with yourself – maybe there’s some truth to their concern about your dedication to video games. So perhaps the compromise could be, for example, that you will agree to do something else with the time that you would have spent in church instruction on those Thursday afternoons. That is, not video games (perhaps), but not church, either. Of course, one of the other major parts of growing up is then living up to whatever promised you’ve made as part of the negotiation.
This is part of growing up: Learning to navigate the obstacles and requirements that others put in front of you as you manage to go your way. The worst thing that you could do here is to go “because they make you” and then sulk about it. That would demonstrate that you really aren’t ready to grow up yet, so don’t do that. (Running away isn’t a good choice, either. Not that you’ve expressed such an intent, but just in case that comes up. Running away certainly demonstrates a clear desire to “go your own way”, and boy howdy does it ever, but it generally doesn’t include the “reasoned argument and negotiation” parts, either.)
While I’m at it, another part of growing up is recognizing reality: your aunt is your aunt, whether you approve of her, or like her, or not. Recognize reality while you’re at all of this other stuff.