I would suggest just assigning your VSTi outputs and then do a Channel Batch Export of all 16 tracks in Export Audio Mixdown. Then instruct Cubase to automatically import the audio files back into the project in the Export Audio Mixdown dialogue under “Import into project”. Done. You can do this faster than real time as well.
While you can record the VSTi directly to audio tracks via dummy busses and routing it is pretty cumbersome with so many tracks at once.
Bounce in place or some sort of extension of the Freeze functionality would be be a welcome feature in Cubase. We have track versions now so why couldn’t just choose MIDI or Audio? Anyways, this subject has been discussed here forever on the forums.