help interpreting traffic graph data

I am not a technically oriented person, but have been tasked with helping resolve ongoing utilization issues with a fairly large circuit. I have looked online to try and understand what the attached traffic graph is reporting, but would like feedback from experts so that I ensure I am not misunderstanding.

The speed is calculated at 14.97 Mbps. The vendor for this service is claiming that utilization of the bandwidth is hovering between 70-80% per day (and if you add the averages for the week depicted, it is right at 75%). The total amount of data during this reporting sequence was 613 GB IN and 240 GB OUT. I am trying to determine if the amount of data over 7 days at that calculated speed is really that % of use. Is there a calculation I can use to verify the numbers?

Assuming that the traffic has been vetted and the majority of it is business related / necessary, and assuming that we would like to add more users, I don't see any solution but to add additional bandwidth. Am I reading this right? Also, can anyone explain to me how to interpret/understand the 'Max: %' number in the graph? I am unsure what that is telling me.