Hi there, I’m suffering the same orbit lag on my macbook pro Retina (mid-2012). There is nothing related with the complexity of the model but maybe with some incompatibility of SketchUp 2016 with the new graphics driver upgrade in this new OSX version…?. It shows a laggy behavior too with move, extrude and other tools when you have to interact with objects in the viewport.
The issue began immediately after upgrade to the new version of OSX El Capitan V.10.11.4. I made a downgrade to OSX V.10.11.3 and after that the lag disappeared completely. Until this can be fixed I’m thinking in wait sometime before upgrade to the new OSX version again…