Open iMovie, go to the top menu, click iMovie > About iMovie , and confirm it says Version 10.2.5. System Requirements for 10.2.5

Users noted faster export times, especially when working with HEVC (High Efficiency Video Coding) formats.

Locate iMovie and click . (If you are already on a newer version, this option won't appear). Option 2: Using the DMG File If you have sourced a legitimate iMovie_10.2.5.dmg file: