No, I didn't. But I did find the cause: I had set the source folder so that it would sync from the external hard disc, which contains the backup but is an HDD. Syncing from the computer's own SDD goes a lot faster. Thanks for replying.

Did you enable Auto-Conversion as this will slow down the process?

Syncing my phone always used to go very fast, but now it's going very slow: more than 10 seconds per song (some 3MB on average). See my signature for the hard- and software details. I'm doing it over a USB cable and the computer of itself is very fast, as is the phone. Thanks for any suggestions.