Hello,
It is *incorrect* to say: "Orthanc supports up to 15TB storage".
The correct assertion is: "Nobody in the community has ever reported a strong limitation of Orthanc with respect to large datasets", provided the recommended setup is used:
There is nothing in the source code of Orthanc that would prevent the DICOM database from growing to dozens of TB. The pressure would actually be more on the database engine (note that PostgreSQL is highly recommended) than on Orthanc itself, especially since release 1.9.2 introduced the possibility of having multiple Orthanc servers sharing the same database (which allows to deploy a cohort of Orthanc servers in order to lighten the workload on each of the servers).
We need testimonials from the community (including from your team) in order to refine this information.
In either case, you really should be considering switching from Microsoft Windows to GNU/Linux if you are considering such a large-scale deployment.
Regards,
Sébastien-