SELECT 
  * 
FROM 
  cscart_ble_content_images 
WHERE 
  page_id = 1503 
ORDER BY 
  position ASC, 
  image_id DESC

Query time 0.00067

JSON explain

{
  "query_block": {
    "select_id": 1,
    "read_sorted_file": {
      "filesort": {
        "sort_key": "cscart_ble_content_images.position, cscart_ble_content_images.image_id desc",
        "table": {
          "table_name": "cscart_ble_content_images",
          "access_type": "ALL",
          "rows": 1510,
          "filtered": 100,
          "attached_condition": "cscart_ble_content_images.page_id = 1503"
        }
      }
    }
  }
}

Result