The whole point of the subscription is to pay for server costs and to pay the developers to keep developing the game, This game is going to cost a lot of money for upkeep and development. As stated it's only going to be 10-15 a month, basically the cost of a happy meal at mcdonalds or any other fast food place. It's honestly quite a small price to pay for one of the most unique games coming out within the next year or so. It was already discussed that it will be subscription based for a reason and I do not see it changing any time soon, if at all - ever. This isn't one of those games that the devs will release, grab some money and then ditch. They plan on developing this game for many many years, quite possibly 10+ years if the community stays active and supportive. Saying all of such things, maybe if you get good enough after a couple months of playing, there is the chance you may not even have to pay to play anymore as there will be the opportunity to buy subscriptions with in-game money from other players who are willing to sell time.
If you're old enough to get a job then i recommend doing so - so that you're able to play the game with everyone. Hell, knock on a few neighbors doors in the winter time and offer to shovel their driveway for 20 bucks, or even mow a lawn in the summer.. There's plenty of ways you can grab a few bucks to pay for such a cheap game.
Cheers,
Tumeden