Create a new online store or modify an existing one

We have a valid internet mazazine on the Wordpress CMS x-one.pro/. Site traffic is not very large, the server is powerful, but the pages are loaded for a very long time. We turned to a specialist in speed optimization WP, the results improved slightly, but still the pages of product categories and the main one open rather slowly. The results of the site speed test in the red zone. This is felt even without services by every new visitor.

The programmer says that WordPress in principle is not very suitable for the tasks of an online store with a large number of products. Plus, we now have a heavy theme (design template), which loads a bunch of scripts and this slows down the site.

Therefore, the task is: either to achieve good fast operation of the current site, or even to create a new online store from scratch, or on some popular ready-made solution such as the same Bitrix, etc.

I would like to hear your suggestions. Can you offer and implement proven options for large online stores, or find solutions for your current site?