Database query question

[eluser]emperius[/eluser]
I have the following query:

Code:

SELECT
    Object.ID,
    Object.NasPunkt,
    Object.Area,
    Object.Distance,
    District.Value AS District,
    (SELECT Photo FROM ObjectPhoto WHERE ObjectID = Object.ID ORDER BY PhotoOrder ASC, ID DESC LIMIT 1) AS Photo
FROM
    Object
LEFT OUTER JOIN
    District
        ON District.ID = Object.DistrictID
WHERE
Object.Special=1                                                
ORDER BY Object.ID DESC
LIMIT 20

On page loading it takes a long time, even when there are many visitors there's 503 error. In my opinion there's nothing that may take so long time for page loading.

How do you think what may be the problem?