I dunno -- I think people are vastly overestimating the disadvantage citizens from a low TL homeworld would have in an interstellar society like the Imperium. Unless the homeworld is interdicted, if there's at least a class D starport onworld they are probably going to have a basic understanding of the Imperium and higher tech levels.
I would not be surprised if the Imperium actively attempts to engage lower tech worlds in interstellar society. Each of these worlds represent a potential market and source of valuable resources. So maybe the Imperium goes out of its way to recruit and educate these citizens for roles in the military and bureaucracy? Who doesn't love to hear rags-to-riches stories of destitute kids from low tech worlds rising to fame and fortune in service to the Emperor?
I would also contend that Edu means less and less the higher the TL. As TL increases, the complexity and size of the information increases exponentially, creating more and more specialization. Any one individual can only know less and less of the total body of knowledge. And paradoxically, tech becomes easier and easier to use even as it becomes more complex.
On a TL0 world cut off from interstellar society, Edu 12 might mean you know a lot about everything; you've read the primary sources for all major fields of inquiry. On a TL15 world, Edu 12 might mean you know a lot about one specific sub-specialty of a specialty of a sub-discipline; everything else you know comes from secondary or tertiary sources, and you rely on compudatabases like the Imperial Encyclopedia to keep up.
A much lower TL scholar might not be so disadvantaged on a higher TL world provided they have access to all the higher TL shortcuts and aids. They are just familiar with one less sub-specialty.
I grew up in a rural area with a significant number of kids who were raised off-grid and homeschooled, basically TL0. Some were back-to-the-landers and some were from religious families. Many of these kids grew up and went to college and generally fared as well as if not better than kids from TL7 homes. They knew what a urinal was even if they grew up with an outhouse, they weren't frightened by cars or radios. They might not have known who Hall and Oates were or watched an episode of ALF, but that wasn't a significant impediment to their success. In fact, it may have been an advantage.