perhaps, if you tell me what mode (QuickMode?) you are using, I can try something.

Yes, QuickMode.

ok, just a minute...

ok, please download, unzip and copy the file attached into /administrator/components/com_breezingforms/admin/

I raised the amount of chunks, so each chunk is a lot smaller, if your hosting company has trouble with bigger chunks, it should help.
The disadvantage is, that on each save you will get a lot more progress messages than usual.

Thank you for the file !
But the same issue is still present ! Slowness in back end.

I think that I have to quit OVH and move to PlanetHoster...

damn, I am sorry for the trouble