You don't need third-party "high compression" tools that might contain malware. Dolphin has a built-in compressor: and right-click any game in your list. Select "Convert File..." Choose RVZ as the Format.
These ISO files are "1:1" copies. They contain every single bit of data found on the original disc—including data that the game never actually uses. This concept is known as "padding." dolphin games highly compressed