What you need to do, is take a serious look at your story structure and decide how the story evolves and where it ends.
Your story should look something like this:
(Diagram by Christiana Wodtke ())
If you don’t know anything about story structure you may need to do some research at this point.
You probably already have some idea of the Crisis, Climax, & Final Conflict, but given you are only 15k words in, it would suggest you are labouring with the struggle and how that builds tension to the final crisis.
Here are a few tips:
Write down a story outline.
What needs to be revealed between where you are now in the story and where you need to get to. ‘Reveals’ are the information/character changes, that need to be disclosed/discovered by the characters in each step of the journey. Each ‘Reveal’ scene/set of scenes/chapter, should be more intense/important/dramatic than the one before. By concentrating on the information ‘revealed’ at each stage of the story you can plan your way from point ‘A’ to point ‘B’.
Sub/parallel plots, involving minor characters, can also be woven around the reveals of he main story to add interest.
Hope this helps you out of the doldrums.