Hello Ruben,
Unfortunately, due to the style that’s set up for Draft Mode, the Orbit button/feature is removed (as far as I know it to be). This is intentionally done to achieve the 2D CAD styled interface, and it’s important to note that although it will appear to be a traditional CAD interface, it will not function the same as a standard CAD program – meaning that the 3D orbit will not function the same.
You can always generate your scenes after you finish your detail drawings and orbit around in those. We do that often to verify that certain elements are present in the plan drawings. Although it will be a bit different with the scenes that are created from Draft Mode as the stacked viewports will be line weights and fills controlled by their corresponding layers.
On your second issue, the lag could be caused by excessive line segments (if you imported details from another CAD program) – if this is the case, we usually re-draw arcs, circles, and other high-segmented lines in SketchUp to simplify things.
One other thing you can try is purging your model/file. Go to Window>Model Info>Statistics and click the “Purge Unused” button – this will clear all the lingering things that can bog down your model/file.
One last thing you can try is changing your OpenGL Settings. Go to Window>Preferences>OpenGL and uncheck “Use fast feedback” and “Use maximum texture size”. Also make sure your Multisample anti-aliasing is set low (4x or 2x).