Let's try to find out the origin of this slowness. As Java and Java 3D were updated in the recent versions of Sweet Home 3D, I would like you try the following tests with an example of the gallery and with a file of yours:
- Try first Sweet Home 3D 4.6 that uses Java 6u45 and Java 3D 1.5.2.
- Then try Sweet Home 3D 5.0 that uses Java 8u51 and Java 3D 1.5.2.
- Then try again Sweet Home 3D 5.4 that uses Java 8u51 and Java 3D 1.6.0.
- Finally, install last update of Java 8 32 bit (jre-8u131-windows-i586.exe) and run Sweet Home 3D with Java Web Start.
Be sure to display the About dialog at each step to check the Sweet Home 3D and Java versions you run, and if it's in 32 or 64 bit (the used Java 3D version is displayed only from version 5.3).
In your final report, don't forget to mention also the Windows version you use and the graphics card with possibly its driver version.

By the way, if I request to try with an example of the gallery too, it's because I know that some Collada files like this bush are extremely slow to handle in Sweet Home 3D (even after removing the lines that surrounds the leaves in Sketchup).

Many thanks for your patient efforts [:)]