IMHO, the bug report mentioned by @Pedro1 describes a different issue. The question concerns thumbnail images when setting icons to extra large. The bug report concerns the preview pane of Windows Explorer.
Regarding thumbnail images: you can modify the LO config manually as described in this OOo forum thread. I can confirm that this solution works, but you should be warned: you’ll have to edit the config files manually with administrative privileges, which may break your complete LO installation!
If you don’t have experience in editing XML files manually, you should refrain from following that solution. It may be worth an enhancement request in the LO bugzilla system to make those config options available through the UI. (i didn’t check if there’ already such an enhancement request…)