Hi Antonio, first, you are actually in the wrong forum, you should be looking at the backup/restore forum, alternatively, the Quiz forum may also prove helpful. Each activity has its own forum, this forum is about the Forum plugin.
Having said that....
The numbers you give there are what? Quizzes or questions?
If they are the number of quizzes on your site, then someone has been very busy. If they are the number of questions, than have you considered taking backups just of the questions? Can you do that?
From memory, quiz questions were saved in the moodledata folder in v1.9 so can you save it as a zip and resort it as an SQL file? I am pretty sure you could enter questions directly into the database... as long as you were to populate all the right tables. To do that, you may be able to create a template from the original restore file and upload it directly to the database via phpMyAdmin or Moodle Adminer. Or perhaps generate a new backup from the v2.1 and use that as a template.