Version 14 first included the network synthesis capability (in the project pane, expand the Wizards node and double click on Network Synthesis). An important missing piece was the ability to synthesize circuits using vendor component models. Starting in version 15, you can now include vendor components in the synthesis.
When you start the wizard and go to the Components tab, there are new choices for the Series component type and Shunt component type, and a new button to Select Components.
The next dialog will allow you to browse any library you have loaded, whether it be the online vendor libraries, a local copy of the vendor libraries, your own library of parts, or a PDK library.
Below are some parts selected for synthesis.