For post-interview applicants -> acceptances, rejections, and WL released on 15.
I've seen batches of rejections a little pre-15 and post-15 for pre-interview applicants; all dependent on the school.
The OUWB adcoms specifically let us know that they'd begin sending post-interview rejections out before October 15th, citing traffic rules. So it's definitely possible that rejections could go out a bit early, depending on when adcoms convene.
Agreed. A rejection, at the very least, is feedback and gives you the option to contact schools, use that to find the problems in your app, and prepare for the next cycle if necessary. Silence from schools just sucks away valuable time that you could be using to do something palpable. Moral of the story, don't fear or view an Oct 15 rejection as necessarily bad. 10/10 times I'd choose getting rejected now as opposed to later.
From my casual scanning of last years school specific threads, it appears that news is delivered mainly to post-interview candidates. FWIW, I got an II on the 15th last time I applied so it'll be a "refresh your email" kind of day regardless.