What does it mean if my WBC count 15000?

Depends on symptoms. An elevated WBC can mean infection or a number of other things. 15000 can be normal in some situations. It is important to describe any new symptoms that you may be experiencing. This will help in determining if the elevation in wbcs is normal or a sign of something more serious. Please follow up with the provider who ordered your cbc.
See below... A common cause of increased WBC is represented by infectious/inflammatory conditions; however, other clinical associations are possible including more serious diseases like leukemia. It is important to know what type of cell causes the increased wbc. Is it because of an increase in neutrophils or lymphocytes? A CBC with differential and morphology would be a reasonable next step.