Hello, @Marta,
We recommend that you do not show all products (-1) on the Shop page at once (Theme Options > WooCommerce > Shop > Shop page layout), as it seems your server cannot handle this request for more than 1 thousand products. However, the option was still enabled https://prnt.sc/Cv-VOw_PrnpD . We have set it to 16 https://prnt.sc/Sp9O1Z_cVedz and enabled the option Customizer -> WooCommerce (Shop) -> Shop -> Shop Page Layout -> Pagination Type to the value Infinite scroll. This has significantly reduced the load on the shop page.
We also recommend that you check the speed without any third-party plugins. The PHP version cannot be the cause of this problem. A change of domain can cause a similar problem, please ask your hosting provider if there are any requests from your new domain to the old one.
Kind Regards,
8theme team