This morning, as the zfs-send/receive had finished its job during the night, I performed the last sync and moved FediMeteo from the previous 4 euros/month VPS - netcup - to a 4 euros/month VPS - OVH, Milano, Italy.
Thanks to #BastilleBSD and the jail setup, it was easy peasy.
So, the weather forecasts are now broadcast from Italy and the performance has skyrocketed - while still being served by a 4 euro/month VPS.
I suspect the netcup VM had been capped by the provider - but I'll investigate.
So...Ciao, FediMeteo!