OK. As far as I researched the WooCommerce provides default pagination for orders in My Account page. See this GitHub issue here. And also see, there is a hook declared at my-orders.php in your code called woocommerce_before_account_orders_pagination by doing
<?php do_action( 'woocommerce_before_account_orders_pagination' ); ?>
So WooCommerce provides default pagination. You better use it. May be it’ll be paginated after the orders number is greater than 15.
Anyway if this thing does not work then you can see this post. This guy says he made it worked with the pagination. Though I’m not sure if this thing work or not cause I haven’t tried it, its worth a try for yourself.
Hope the above answer helps.