Stephen seem´s to give wrong information, as he also send me a second mail:
"Talema Toroid 30VA 2x15V has 2 version, input 220V and input 115/230V version. When using input 115/230V version for 220V input, the 2 primary coils must be connected in series : Brown ,(Violet-Grey), Blue. for 2 secondary coils , connect them in series as red , (black-yellow), orange , to become 15-0-0-15V. As I remember, the DC resistance across each secondary coil is about 1.5 ohms."
But I do not see any difference, still it will be black-yellow as 0V for secondary.