-15 either means that your License Manager (NLM) isn't running or a firewall is blocking it (or the dreaded IPv6 incompatibility issue.)
I have many fixes listed for this in my signature line.
For a Quick-Start Guide on configuring the Autodesk License Manager, please see my post for further information:
For more information about Network License Manager connectivity issues and IPv6, please see my discussion post here:
FLEXnet License Admin | MSI Cleanup Utility | .NET Framework Cleanup Tool | IPv6 NLM Fix | adskflex.opt Options File | Combine .LIC Files | Disk Space