Told I was going to be paid 15/hr by March, currently being paid 13.50/hr.

Hey All, Im 18 and I recently started working at Starbucks (Cupertino, CA). During the interview process for this job I had asked how much the pay would be and the hiring manager stated the figure 15/hr. It was based on this figure that I accepted the job. After accepting the job and waiting 2 whole paycheck cycles I asked her why Im still only being paid 13.50 and not 15. She responded by saying the 15/hr pay rates will be implemented in March. I just got my first paycheck of March last Friday and it's still 13.50, what do I do? Are there grounds for breach of contract? The pay figure she stated was completely oral, as the documents and paperwork I signed stated I would be getting paid 13.50, yet the reason i accepted the job in the first place was bcuz it was 15. Is this battle worth fighting and if so, how do I win?