No - your partner doesn't need to file Schedule C if he/she is NOT in "business" of writing but I recommend that he/she does. A non- match of 1099-MISC data entry may trigger a correspondence with the IRS, and I'm not sure it's really worth not filing Schedule C for $15. Also, since you mention two books... he/she may be in "business" ...
It is taxable income no matter the amount... but if he/she is not in business of writing, you can enter income as line 21, form 1040, but again... the 1099-misc won't match IRS's data entry...
And you can enter tax withheld in box 4, you should have that there.
edited 3/19/2017
