You can interconnect transformer windings in several ways to produce various output voltages. For power and distribution, you employ the conventional delta or wye connection. But for special applications, you can use an other lesser-known configuration: the zigzag connection. As you know mentioned phase shifting in IEC60076 is limited to multiple of 30 degree, but it seems your concerned phase shifting is multiple of 15 degree. Special connection of zigzag connections can be used for 15 degree displacement. Selection of suitable ratio of broken phase in zigzag connection can cause desirable phase shifting. You will typically find the windings on each phase of a zigzag transformer in two halves. These winding halves interconnect to obtain a zigzag arrangement. 
As an important phase shifting application we can note to harmonic elimination term. The best way to eliminate harmonics is to use a technique known as