Revit 2015 uses the (product key + serial number). If you have a valid perpetual license from 2015, you can activate it online or offline.
Autodesk has officially ended support for Revit 2015. This means no more Service Packs, no security hotfixes, and zero technical support from Autodesk if the software crashes. If a Windows 10 or Windows 11 update breaks the software, you are on your own. revit 2015 downloads
Revit 2015 was built for a different era of computing. While it runs on modern machines, you may face driver compatibility issues, particularly with high-end graphics cards (GPU). You might find yourself spending hours tweaking .ini files just to get the ribbon to render correctly. Revit 2015 uses the (product key + serial number)
If you already have the software but are missing standard families (windows, doors, templates), you can download the content libraries separately: This means no more Service Packs, no security