Comment 26 for bug 1491064

I have this same issue, and I have found that it is exactly related to what su_v pointed out previously. To recreate the issue:

1) Set up Inkscape so that when it's launched the Text and Font dialog/panel is NOT open (e.g. close the Text and Font dialog before closing)
2) Close Inkscape
3) Open Inkscape and load a large SVG with lots of elements
4) Create a new text element and start typing -> Result: Typing is fast
5) Now, openthe Text and Font dialog/panel (Shift+Ctrl+T)
6) Create another text element and start typing -> Result: Typing is incredibly slow

Hopefully that's helpful