On my blog site, there are totally 4058 posts. After installing WPML CMS, it is a bit slow if I click "English" to show the ENglish post and other languages tags to show those in other languages.
So, I just wonder if you have a recommended system configuration for WPML, including how many physical memory should be used?
You can check WPML minimum requirements here https://wpml.org/home/minimum-requirements/
Beside this, we don't have a recommended configuration, it all depends on your site, how many plugins are you using and what kind of hosting do you have.
If you have a large site on a shared hosting it might be expected that WPML slows down your site. Without further information, we cannot say anything else.