I finished my 15 days vibramycin-d (doxycycline) course yesterday, when I shoud be retested for chlymedia to make sure it's cured?

Generally not done. The treatment for male chlamydia is actually 10 days. Are you still having symptoms..Because generally we don't retest for chlamydia. Also, just so you know, guys can have chlamydia without symptoms. What i would say is if your symptoms are totally gone, your probably just fine.
CDC recommendation. Women and men with chlamydia should be retested about three months after treatment of an initial infection, regardless of whether they believe that their sex partners were treated.