can me and my girlfriend get married without parent consent?

In Oklahoma the court can authorize a marriage of a girl under 16 if the court conducts a hearing at which the parents can present evidence in support of their objection.  This might not be the smartest thing for you to do if you were 18 and she was 15 when she got pregnant because you would be confessing guilt to the crime of rape in the second degree, which is a felony punishable by 1-15 years in prison.