Server: Severe scalability problem

Hi,
I am running owncloud 8.1.3 with the current ownnote plugin on vm using 3 of the 4 cores of my xeon and 3GB of RAM.

I imported about 1800 Notes from evernote to ownnote.
And even days after the conversion is finished ownnote still is unusably slow.
Opening the notes page takes about 1 minute before notes are displayed.
If I delete a note (which by the ways should be possible if the note is open, too) it takes about 60seconds with almost no cpu usage until the UI is updated. Same happens on chaning a note.

As the import process lost most of my categorizations I would have to sort my notes again, which would take roughly 1800x2 minutes ....