How to speed up the filtering of a large number of products on the site?

Question

opencart

Good afternoon!
Tell me how to speed up the filtering of a large number of products on the site?
So far, the site has about 10,000 products, divided into categories and subcategories. There is a product filter on the category/subcategory pages. When there are less than 1000 products in the filter, it works fine, but when 2000-4000, it loads the products themselves quickly on the page, but updates the filter attributes of these products slowly.
It is planned to add more goods and there are suspicions that it will take even longer to think.
How can you speed up requests and processing of a large number of products?