The official way to download OS X Yosemite 10.10.5 is through Apple Support
https://updates.cdn-apple.com/.../InstallMacOSX.dmg mac os x yosemite 1010 5 download dmg link
: If the download links do not trigger immediately, try using the Safari browser The official way to download OS X Yosemite 10
If you need Yosemite:
: Ensure your Mac has at least 2GB of RAM and 8GB of available storage before attempting the install. Download OS X Yosemite 10.10.5 Combo Update mac os x yosemite 1010 5 download dmg link