I think that is not possible. But maybe you like to set e.g.:
'preview_max_x' => 1024,
'preview_max_y' => 1024,
I think that is a good restriction.
Also you can use to update:
sudo -u www-data php occ preview:delete_old
sudo -u www-data php occ preview:generate-all
You can also read this thread. I do not fully unterstand it. I also find this comment in an issue.