Investopedia explains 'SEC Form 15'
When a company files an SEC Form 15, it usually means one of two things. It may mean that a company is ceasing to exist in a publicly-traded form, either returning to privately-held status or going out of business altogether. Alternatively, it may mean that a company is simply canceling a certain class of securities, replacing them with another class.
Related Forms: SEC Forms 15-12B, 15-12D, 15-12G, and 15-12F.