So that plugin probably causes the problem. Could you recommend us any other plugin to compress and reduce size images?

Just set your gallery settings accordingly for maximum sizes and let CB Gallery handle it. If you want better image compression and performance contact your host regarding getting ImageMagick installed and use it.

When you open a photo in CB GALLERY and click on the arrow to the next image it takes some time to load it, is there anyway to speed up it?

It's because you have very large fullsize images uploaded. Adjust the maximum size parameters within CB Gallery so future uploads aren't so large to improve performance.

Please tell us more about what causes the problem please, the only thing we did in joomla was installed that plugin www.imagerecycle.com . Now it is desactivated, so we can not use it?

You don't have to do anything more. The issue has already been fixed. You can continue using that plugin if you want to. It's entirely up to you.

Our demo site provides full backend and frontend access. Login to backend on our demo site by clicking "Administrator" under the "Login As" header. You can then review its CB Gallery configuration directly and compare to yours.

I don't know what more to suggest, sorry. Your site appears to have performance issues in general. The HTTP requests alone for your home page take over 20s. Your activity stream takes over 40s. Consider using caching extensions like JCH Optimizer to try and optimize the headers and use lazy loading for images. Could simply be your hosting package isn't enough to handle what you're asking of it and may need to upgrade to a better hosting package.

I did notice there was a double HTTP request when using the navigation and am fixing that, but that'll only get you maybe a couple millisecond performance boost. Once the modal window loads it attempts to load the image so that's 2 HTTP calls as well. Need to see if I can output the image without doing another HTTP request, but it's unlikely. This isn't likely to give you much of a boost though since your site seams to suffer from performance issues in general.