I think 25 subscribers in two weeks is excellent, actually. The thing with Tapas is that initial growth is very slow. The first couple hundred subs may take months to come, if they come at all. After that, once you get into the popular visible area of Tapas, and you keep updating regularly, more subs will start coming in. But it can take months or years to get any significant number of subscribers.
You need to ask yourself, are you writing these stories because you want to write them, and you're going to continue to write them whether they're popular or not, just because you need to get the story out? Or are you writing this story exclusively to get subscribers and popularity? I think figuring out your own motivations, and adjusting your expectations accordingly, might help out.
If you're writing your story for yourself, just because you want to tell the story, then it doesn't matter how many people subscribe to it - every chapter you put out, your are accomplishing what you set out to do!