1. Use Template>Architectural Glass>Reflective instead of "real" glass, as the "Real" glass is trying to make the decorations appear to be made from solid glass, and not a thin glass shell.
2. Set Light Emitter material to "Fake Emit". This will instantly make the scene render much more quickly.
3. Put Point Light inside of your light components.
1mm radius
power of 5 watts
Turn off soft shadow
Turn off shadow for these lights to make them render nearly instantaneously.
4. Use "Bloom" in "Post Process" panel to make the lights have a "glow" or "halo" effect.
5. Copy a slightly smaller sphere inside of the spherical ornament and also make it the Architectural Glass Reflective, so that there are more reflections on that ornament.
6. Set Sky to Background Color so that the render engine ignores the sky settings while rendering. And Disable the Sun for the same reason.
7. Delete lights that are too close to the back wall. Or carefully position all lights for best lighting effect.
8. Place Christmas Light component at original origin of scene, explode - select all of component parts and make new component - this is to eliminate strange scaling issue and odd component axis position and orientation of the Christmas Light component. After making new component, place this on the tree delete the old ones. Use Twilight V2 Pro Proxy Tool to place the lights on the tree quickly if you have Twilght Pro.
9. eliminate ceiling light inside space
10. For Light Bulbs: Try Emitter, set to FAKE EMITTER 40 Watts per meter Squared. Set material to be 5% opacity in the pulldown at the bottom of the Twilight material editor. This increased rendering to 1m17s
In this case just delete or hide completely the geometry inside of the light bulb.
(by mistake the glass on the light bulb was hidden in the last rendering and attached file - open the component in SketchUp and unhide the glass)
Adjustments made in the scene attached. It renders in 21s on Low render setting.
11. Play with different bloom settings they can make a giant difference when the light bulbs are fake emitters.