My daughters have both been through speech therapy (as well as myself as a child), and while I'm not an expert in the field, my opinion is that the number of hours in therapy per week is less important than the amount of practice outside of therapy and the length of time (measured in years) in therapy.  I don't think solving speech problems can be addressed easily and quickly - it takes time and practice.  And the practice can be done outside of the (expensive) therapy sessions.

My child was delayed terribly in speech..he could not speak clearly at all at age 3, and did not finish any of his words, making it impossible for people to understand him.  He received 3 hours of speech a week for a semester, and made great strides.  Be patient. It took around 2 years for marked improvement.  My child is 11 now and you would never know he ever had a problem.  More is not always better, it is the quality of speech he receives, not the quantity.  3 hours a week is sufficient.