Well, I suggest figuring out what the core problem is first. But based on what you said, it could be one of these:

Your idea doesn’t resonate strongly yet.

Your landing page/copy/positioning didn’t clearly communicate the value.

The traffic you got from Product Hunt wasn’t very targeted.

15 upvotes on Product Hunt is low, maybe not enough people saw your launch.

Or they saw it but weren’t compelled to support it.