Hello ms-lara,
Wow it is great to know you have those many contents.
It is specially 2,000 categories that causing memory problems.
Please do contact us from here , there need to customize a code in the theme.
The code need to customize is https://themes.trac.wordpress.org/browser/supernews/1.2.1/acmethemes/customizer/custom-controls.php#L33
Best Regards!
Acme Themes