SELECT 
  content.*, 
  templates.priority 
FROM 
  cscart_cp_seo_templates as templates 
  LEFT JOIN cscart_cp_seo_templates_content as content ON content.template_id = templates.template_id 
  LEFT JOIN cscart_cp_seo_templates_objects as objects ON objects.template_id = templates.template_id 
WHERE 
  templates.status = 'A' 
  AND templates.type = 'C' 
  AND templates.company_id = 1 
  AND content.lang_code = 'ru' 
  AND (
    objects.object_type = 'C' 
    AND objects.object_id = 219 
    OR is_default = 'Y'
  ) 
ORDER BY 
  templates.priority DESC

Query time 0.00147

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "templates.priority desc",
      "temporary_table": {
        "table": {
          "table_name": "objects",
          "access_type": "system",
          "possible_keys": [
            "subscriber_list",
            "template_id",
            "object_type",
            "object_id"
          ],
          "rows": 0,
          "filtered": 0,
          "const_row_not_found": true
        },
        "table": {
          "table_name": "content",
          "access_type": "ALL",
          "possible_keys": ["PRIMARY"],
          "rows": 4,
          "filtered": 75,
          "attached_condition": "content.lang_code = 'ru'"
        },
        "table": {
          "table_name": "templates",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["template_id"],
          "ref": ["orbit_cscart_orbit_cscart.content.template_id"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "content.template_id = templates.template_id",
          "attached_condition": "templates.company_id = 1 and templates.`status` = 'A' and templates.`type` = 'C' and templates.is_default = 'Y'"
        }
      }
    }
  }
}