Are Post-Install Windows Slowdowns Inevitable?
Found on Slashdot on Saturday, 27 June 2015

I recently reinstalled Windows 7 Home on a laptop. A factory restore (minus the shovelware), all the Windows updates, and it was reasonably snappy. Four weeks later it's running like a slug, and now 34 more updates to install.
It appears that Windows slows down Windows!
With Windows 10 coming, Microsoft has already prepared to make users move to their latest release, even with questionable ways, such as pushing out an "important" with is basically nagware only. So it would not be much of a surprise if an older OS gets some performance loss; it seems to be common for others too to make you buy a new iPhone.