SELECT 
  value 
FROM 
  cscart_form_options 
WHERE 
  element_type = 'U' 
  AND page_id = 1574

Query time 0.00020

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_form_options",
      "access_type": "ref",
      "possible_keys": ["page_id"],
      "key": "page_id",
      "key_length": "3",
      "used_key_parts": ["page_id"],
      "ref": ["const"],
      "rows": 10,
      "filtered": 100,
      "attached_condition": "cscart_form_options.element_type = 'U'"
    }
  }
}

Result