They should be installed automatically if you checked VS 2015 at installation.
Can you please verify that the registry entries for the toolbox are there?
if they are not, you can: a) run the installer again and select repair; or b) add Wisej.Core, Wisej.Web, and the extensions manually. Don’t add the .Design assemblies.
Let me knowif the entries are missing from the registry or if they are somewhere else.
I have a similar problem with VS2012.
When first installed all the controls for a form are available in the toolbox. However closing and reopening VS causes all the toolbox items to be removed. I re-ran the new installer but it did not fix the issue. I had to manually add the controls back into the toolbox.