How to control the post displayed on a specific category? You can solve this problem by simply copy the codes below on your functions.php file.
function category_blog_posts_per_page( $query ) {
if ( is_admin() || ! $query->is_main_query() ){
return;
}
if( is_category( 1 ) ){
$query->set( 'posts_per_page', 15 );
}
}
add_action( 'pre_get_posts', 'category_blog_posts_per_page', 1 );