So after almost 3 years in Madrid working for the same company, I have just realized that the reason why we are working a shift from 8 to 15 is that allegedly during the other seasons we work 15 additional minutes that compensate the non working hours of the summer.
Curious thing though, because this country I believe is the only one with this kind of schedule in Europe.
The excuse for this, spanish people say, is the high temperatures. Which I must agree and disagree. Spain is not the hottest place I have lived in, but in this moment having a "summer shift" is very convenient.