There have been a number of changes “under the hood” of Renderworks that increase the quality of renderings using the stock settings. Some of the aspects that were improved significantly in this way were Indirect Lighting and Antialiasing. Hence, using the stock settings in 2016 will make renderings take longer than they did in 2015, but you will now get an even better result.
If you would like to reduce the rendering time, you’ll need to adjust (lower) the render settings. Doing this should produce renderings at the previous quality levels and should take similar amounts of time as they did in Vectorworks 2015.