The kind of performance you are seeing, 2.3GB in 1hr 15 mins, is in line with the performance I have seen others achieve migrating to OneDrive for Business from on-premises file servers. The issue is not the bandwidth in your case as you have plenty; its the speed at which SharePoint Online subsequently processes the data after it has received it. The upload would be fast, but the commit of that data by SharePoint Online would be slow.
To achieve better overall performance you could try uploading in parallel on the same computer or ideally different computers. For example, migrate 100 students' to OneDrive for Business on one server, and another 100 on another server.
I recommend reading this article by Andre Kieft (from Microsoft) on migrating to OneDrive for Business. It's not about performance but more about the kinds of gotchas and issues you could run in to and how to resolve them when migrating from file servers to Office 365: Migrating File Shares to OneDrive for Business - Share-Port - Site Home - TechNet Blogs
I also have a free performance calculator you can plug your numbers in to give you a rough idea of migration times here (on the right hand column): Migration calculator