plasma workspace very slow at startup

[Luca Ferrari]

Hi all,
I'm running 15.10 up-to-date. When I login plasma I see it very slow
in becoming "ready". In particular I have only the wallpaper for
around 1 minute, then the panel drawn in a strange way (icons very
small and all on the left, even the clock is in the left middle of the
panel), the disk spins for a few minutes and then the panel rearranges
itself to the right size and position.
Then the desktop is usable, but it tooks about 2 minutes before I can
start working.
Any idea about what should I search for?

Thanks,
Luca