Hi Jojo,
I'm going to have two chapters that are (approx) 20, 000 words each, but they are my 'analysis' chapters. Each 'lit review' chapter didn't exceed 10, 000 words.
What chapter are you working on (lit review or analysis)? If it's a lit review, and you are only half way through and already hitting 15, 000 words, you might want to consider being more concise. BUT ... keep writing because you can always edit later (and I'm sure you'll be able to use bits elsewhere ... OR ... you could eventually end up splitting the chapter into two.
My advice ... keep writing if you are happy with what you've got. Your supervisor will advice you what they think is best (... they should have a clearer idea than you about how your overall project is going to 'shape up'!).