Should one uograde to KDE 5.2.2, and if so how should one do it.
There is no KDE 5.2.2 .
KDE is the Community.
If you mean Plasma 5.2.2. There is no update available in the repo.
Never the less most of the fixes are already in our plasma release shipping with Netrunner 15
Tue, 24 Mar 2015. Today KDE releases a bugfix update to Plasma 5, versioned 5.2.2. Plasma 5.2 was released in January with many feature refinements and new modules to complete the desktop experience.
Netrunner 15 shipped many of the bugfixes of 5.2.2 already plus a few more in its release.
Since there will be no backport from Kubuntu since utopic is no LTS system, Netrunner 15 will stay as is. That means if nothing is severly broken, keep it running until you might want to upgrade to “vivid”. 
Personal note (these are my 2 cents, to each one is different):
Its a bit like Windows7: Dont update if its running fine unless you have to (and imo don’t fall for all the security hype, as one can never have a 100% secure system anyway, so chances are either slim/random or you are targeted specifically then there is always a security hole at risk or you need a special hardened stealth-system).