Both pg_field_type and pg_field_name are called a ton on every page. They are typically extremely fast but they are still load on the db for something which is static in many situations. pg_num_fields might also be in the same boat.
The driver here is not really increasing an individual page load but the total sql load.
I suspect it's not possible to use MUC, and it would just shift load to redis etc, so probably the way is directly into apcu and behind a config.php option.