To understand why the 2015 version remains popular, it helps to review the core features that Autodesk introduced in this specific release:
AutoCAD uses DirectX 11 or OpenGL for 3D visual styles (Shaded, Realistic, Conceptual). These rely on GPU drivers installed on the host system. A portable version has no way to guarantee that the graphics card on a borrowed computer will be compatible. At best, you suffer lag; at worst, the program crashes on orbit. Autocad 2015 Portable
However, the experience is often far from seamless. To understand why the 2015 version remains popular,