I've been doing a 52 book challenge in 2015, so far I've only managed 5 SK books of the 40 I've read, will squeeze in a couple more before the end!
I put together an Excel list recently to keep track of which SK books I'd read and what I still need to get to. To my surprise taking into account novels, co-written novels, Dark Tower novels, short story collections, novellas and non fiction, that added up to around 75 titles of which I've only read a piddling 31. Less than half! 2016 is the year I put a big dent in that.