Looking back and averaging the number of pages per chapter for Spirit Walker, I come to 22.6.
If you have done 15 pages, that means you are (according to the laws of averages) about 66.371681415929203539823008849558% done.
At the time of your post, it had been 70 hours, 43 minutes since the last chapter was posted, or 4243 minutes.
That makes a rate of 0.015642630548180344930432007742059% completion per minute.
That makes the total time to complete the chapter 6392.78666... minutes, or 106 hours, 32.78666... minutes.
So, if the laws of averages hold true, the next chapter should be out on April 25, at 1:32 AM.
...
But that's not going to stop me from checking every half hour.
And good luck on the Finals. Hopefully, you won't need it.
Go ahead. Ask me any question, but if it needs logic or intelligence, you will want to ask that brain thingie that lives in in my head instead.