Pages and posts are identical in performance at first, as they are loaded from the same table: wp_posts. However if the theme is including in the render for the page widgets or meta or taxonomies, they could vary greatly on performance, but a priori can’t be affirmed one or other is more performant.
It is really a matter of the render and assets that your theme is including. For example a post could be very fast to load and other post in the same could load tons of resources. Same thing for pages. They are basically the same by themselves.