Adding a section templates to a page via templates element and shortcode element slows down the loading of the page

I have a site where we added a template for a section that we need to add to more pages.

I used the template element and added the template to the various pages. I noticed that the pages are slow and decided to replace the template element with a short code, which rendered the section a bit faster than using the template element, but it was still slowing down the page load.

I then copied the section from the template directly into the pages and it loaded MUCH faster than adding the section via the template element and the shortcode element.

I really want to use a template to enable us to update the content only in one place if needed.

Anyone else experienced this problem? Is there a reason why the template and shortcode elements slows down the loading of the page?