functions.php

<?php

function itsme_editions_ppp( $query ) {
    if( $query->is_category() && $query->is_main_query() ) {

        if( !$query->is_paged() ) {

            $query->set( 'posts_per_page', 10 );

        } else {

            $query->set( 'offset', 10 );
            $query->set( 'posts_per_page', 15 );

        }
    }
}
add_action( 'pre_get_posts', 'itsme_editions_ppp' );