yes, the builds for gen are single streamed. code generation though can be multi-threaded if you utilise GuardIEn for builds and set the relevant parameter(s). (so a server side build and not client side)
We found that on a 2.2GHz or lower VM that builds were real slow. Going to 3GHz+ and having storage as SSD or even making sure windows indexing is on for the relevant folder, does help greatly in build speed.
Also depends on what you are generating ... are you building cobol, java or C#. You can tweak some of the compile parameters in the scr files but you will be still bound by the limitations of what your underlying hardware is capable of.