Installing Visual Studio 2017
You can create an offline installation files for Visual Studio 2017; the steps are documented at https://docs.microsoft.com/en-us/visualstudio/install/create-an-offline-installation-of-visual-studio The good thing this time is that we can run the vs_sku.exe –layout subsequently to update the installation files.
If you are seeing that installing or modifying the Visual Studio 2017; from the offline folder is still downloading the content from the internet; there can be two reasons; either the certificates are not installed as documented in the URL above; or you installed it in the “online” mode the first time; so uninstall it first…and then reinstall from the offline folder after importing the certificates. Once done this way; modifying the installation later adding more workloads etc; it will continue to use the contents from the offline folder
The tip is; that you delete everything in the %TEMP% folder before installation; and then do –layout folder thing (—lang en-US) and it will update the offline folder and create a log file in %TEMP% folder; check the log file ensuring that its saying everything went smoothly. Install JDK and Android SDK / NDK yourself if you want them at folders of your choice (in case you are using Android Studio and dont want multiple JDK/SDKs) and unselect JDK and Android SDK etc during installation (workload details)
Secondly; if you are planning to uninstall 2015; uninstall the Dotnet Core Preview tools first and then uninstall Visual Studio 2015