Opencart mysql query optimize
The reason for slow down of query is clearly visible in the query plan. There are columns need to be indexed, to tune the query performance. In your query you have used oc_order_option table which does not have order_id column indexed. Index it using following command:

ALTER TABLE `oc_order_option` ADD KEY `OrderID` (`order_id`)


Same thing is happening with oc_order_product and it needs to be tweaked with following command:

ALTER TABLE `oc_order_product` ADD KEY `ProductOrderID` (`order_id`)


Also you need to tweak oc_order as well, use following:

ALTER TABLE `oc_order` ADD KEY `OrderStatusID` (`order_status_id`)


After implementing the tweaks run your query and see the performance difference.