As I said I'm actually using Local Info Only on LAN, so the scrapping website isn't in the issue: I do not scrap, ever, on previous sd/kodi I was doing the same but via usb. But It looks like I found the issue : I just switched on a modern sd and I found back a correct speed. Maybe the fact I ask to scan more local files than people using regular scrap was even more slow than usual...
PS: I use TinyMediaManager on PC to scrap my lan files