you don't have to do the text to path conversion with every update of your sgf. In most cases it is sufficient to only do it once, after all your frames and transitions are set up. It's no problem to use text objects in Sozi unless you use an excessive amount of differently scaled text.
So just use your original file with text objects to create your presentation. After all frames and transitions are set up,
- make a copy of your sgf (I use "File"-> "save copy" in Inkscape)
- do the text to path conversion and save
- enter Sozi again to trigger a rebuild of your presentation html (will be done automatically)
As I mentioned above, the actual problem for Sozi (or more specific, the underlying chromium render engine) are different text sizes. So if your presentation zooms in and out a lot you will have to adjust text sizes, which eventually will make transitions more and more sluggish. This will be fixed for the final presentation with the text to path conversion, but it might become annoying when it starts affecting your creation workflow.
From my experience, up to 50 font sizes are no big deal. At 100+ it becomes unusable for me.
To keep it stable, I usually restrict my presentations to a fixed set of text sizes. (Which btw. also keeps me from zooming in and out randomly for the sake of the effect )
If you really need more font-sizes, you might do the conversion for those parts of the presentation which are really settled.
Hope that helps.