Hi @elavarasan16,
The manifest only needs to specify the lowest level SKU - all higher levels SKUs are automatically supported. So there’s no need to specify Enterprise specifically.
However, the version specification in the manifest is for VS2017, not VS2015. There are separate installers for SonarLint for VS2015 and VS2015, with separate entries in the Visual Studio Marketplace (SonarLint for VS2015 and SonarLint for VS2017).
Could you check that you are definitely running the VS2015 installer please? The file name for the VSIX will end with either -2015.vsix or -2017.vsix, depending on the version.