There is another way, if you can;t modify in internal connections
you can use a capaitor with the following arrangement
1- the connection should DELTA
2- the delta poles are A,B,C
3- L1 is connected to A, N is connected to B, the capacitor is connected to A and C
this should do the trick
Regarding the capacitor rating, frankly i don't know the calculations, maybe Mr.Spir (My mentor) can help with this.
Dear Mr. Nael ;
We use this solution for some small & special application ( not 15kW ) where thers's no possibility to have ” 3 phase + neutral “, noting that if there's inside a motor the torque will ne be stable.