## JavaScript (ES6), <s>31</s> <s>29</s> <s>28</s> 22 bytes

    s=>(15-`0x${s}`%15)%15

Port of @xnor's Python answer, except that JavaScript only has a remainder operator rather than a modulo operator, so I can't do it in a single step. Edit: Saved 6 bytes thanks to @Arnauld.