Hi USAeshopFrance,
It's hard to say if you should upgrade or not, as that can be somewhat of a personal question. For example, not all upgrades are smooth. I can suggest that you upgrade, and you may run into hours of troubleshooting and frustration, or you could have a easy 5 minute upgrade. It's up to you to decide if your shop would benefit from the upgrade, and if so, if you have the time to do the upgrade.
If it's not broke, don't fix it
Sometimes it is best to take this approach. If your software is running just fine, why upgrade it? Ideally, this mentality is best ONLY if the newer versions do not include any security updates. If there are security updates, it would be a good idea to upgrade.
Opencart 1.5.2 releasedOpencart 1.5.2 was released on March 03, so it's been out for two months now. If you look at the link in the last sentence, you'll see that this new version of Opencart has added, changed, and fixed quite a few bugs. If you read over that release article and any of the items seem very important to you, then you may want to look into upgrading.
I know I didn't directly answer your question, but I hope I at least helped point you in the right direction. If you have any follow up questions, feel free to post a comment at the bottom of the page.
Thanks,
- Brad