Yes, Facebook is only showing you 15% of what your friends post
Because they want you to pay to "promote" stuff on FB.
As their advertising head, Gokul Rajaram, explained, if you want to speak to the other 80 to 85 percent of people who signed up to hear from you, “sponsoring posts is important.”
In other words, through “Sponsored Stories,” brands, agencies and artists are now charged to reach their own fans—the whole reason for having a page—because those pages have suddenly stopped working.
This is a clear conflict of interest. The worse the platform performs, the more advertisers need to use Sponsored Stories. In a way, it means that Facebook is broken, on purpose, in order to extract more money from users. In the case of Sponsored Stories, it has meant raking in nearly $1M a day.