Will I loose my projects (7 books to print of 265 pages each which mean a lot of work) if I upgrade from iPhoto 7 to latest version ?

The difficulty is that when you upgrade, the newer version may have changes to the templates, and so there will likely need to be touch ups to your books. But there is no reason why they should be lost.

Of course, before upgrading anything: Back Up First.

Personally, I would also make an independent back up, just in case:

Most Simple Back Up:

Drag the iPhoto Library from your Pictures Folder to another Disk. This will make a copy on that disk.

Slightly more complex: Use an app that will do incremental back ups. This is a very good way to work. The first time you run the back up the app will make a complete copy of the Library. Thereafter it will update the back up with the changes you have made. That makes subsequent back ups much faster. Many of these apps also have scheduling capabilities: So set it up and it will do the back up automatically.

Example of such apps: Chronosync- but there are many others. Search on MacUpdateor the App Store

There's a good chance that some of the themes that you used in iPhoto 7 are not available in iPhoto 9. These are the themes available with iPhoto 9.6 and Yosemite:

I don't know if there are any different themes in the lower iPhoto 9.x versions.