The previews are created by plugins.
The following command will list all of the respective description files:
#> grep "ServiceTypes=ThumbCreator" $(kde-config --expandvars --install services)/*
If you open them they have a line which says which MIME types they are for.
You can copy any to your user's services directory
#> echo $(kde-config --localprefix)/share/services
And modify that copy.
If you want to remove previews for the listes MIME types, you can just add a new entry to the file like this
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Source code
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1
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Hidden=true
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Cheers,
_