You can try but there is no guarantee it will run. AC 16, 17 and 18 are the only officially supported ArchiCAD versions for Windows 8.1:
http://helpcenter.graphisoft.com/technotes/operating-systems/compatibility-notes-to-archicad-on-wind...
Loving Archicad since 1995 - Find Archicad Tips at x.com/laszlonagy
AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac28
