Created attachment 429134 [details, diff]
Patch to fix problem
Memory leak in qtdeclarative. Apparently fixed upstream in 5.6. Following reference from Fedora: https://bugreports.qt.io/browse/QTBUG-48799
I have successfully applied the attached patch to 5.5.1-r1.
how serious is the memory leak?
I was having problems with the responsiveness of Plasma, but I think that was related to the activities of the indexing daemon. The memory on my machine was being consumed, but I didn't go to the trouble of finding out the rate of loss. Once I came across the bug report in Fedora, I created the attached patch and updated my local installation of qtdeclarative.
Since installing the patch, and restricting the file indexing, I am happily using plasma-*-5.5.5 without any responsiveness or memory resource issues.
5.6.0 is in tree.