"AutoCAD LT 2015 Is Already Installed" Problem - Autodesk Forums
Many "bugs" in the 2015 version are resolved by installing the cumulative service packs. Service Pack 2 autocad lt 2015 download fix
For valid license owners, the Autodesk Virtual Agent remains the only safe source for the download, and compatibility mode plus legacy runtimes are the only reliable fixes. "AutoCAD LT 2015 Is Already Installed" Problem -