After upgrading to OS X 10.10.3, you may find that navigating the Finder can be arduously slow at times, where the contents of folders you open may take a while to display, and otherwise scrolling and navigating may be overall sluggish. If this occurs, then you can likely fix it by clearing some Finder-related cache information from your Mac.
Caches are small databases of frequently accessed resources that a program can access far quicker than having to locate and parse this information directly from locations on disk, or which store specific URLs and other Web resources that a program may use for accessing an online account or other data. While they usually enhance performance, if damaged then caches may do the exact opposite.
Next, try manually clearing some of the caches that may be relevant to the Finder. These include those for the Finder as well as related services like iCloud Drive. The caches for these services are located in your user library, so get to them by holding the Option key and choosing Library from the Go menu in the Finder. In the folder that opens, go to the Caches directory. In here, consider removing the following cache files and folders:
- CloudKit > com.apple.finder
- CloudKit > com.apple.clouddocs
- CloudKit > com.apple.CloudDocs.container-metadata
- CloudKit > CloudKitMetadata
- CloudKit > CloudKitMetadata-shm
- CloudKit > CloudKitMetadata-wal
When done, log out of your user account and log back in, or optionally just restart your Mac, and see if the Finder slowdowns persist.
A second factor that might be at play here is Apple’s Spotlight indexing routines for Finder searches, where after upgrading or updating a system, Spotlight may attempt to index new items and get hung up when doing so. To clear these problems, you can force your Mac to rebuild the Spotlight index by adding your boot drive to Spotlight’s privacy list, followed by removing it. This may then take a few hours to rebuild, but after which the Finder and services that use Spotlight indexing may show faster performance.