For example, with the Mono kitchen set, the files in muranomobilia site were in size as follow:
murano_mono_airpump.package 360.753
murano_mono_chair.package 176.494
murano_mono_counter01.package 485.265
murano_mono_counter02.package 521.356
murano_mono_counter03.package 531.801
...
And in TSR they are only:
murano_mono_airpump.package 190.459
murano_mono_chair.package 31.550
murano_mono_counter01.package 63.478
murano_mono_counter02.package 311.753
murano_mono_counter03.package 84.676
If those numbers are correct, then the files were simply run through the Compressorizer. I know this because I had those original, giant files and ran them through the Compressorizer myself a few months ago to put them in my game. My files are the same size as those on TSR. And they look just as good in-game now as they ever did. This is why the Compressorizer rocks.