A .7z file is a compressed archive created with software. This specific "pack 1522" name doesn't correspond to an official Dropbox feature. Instead, it is likely a user-uploaded bundle. Depending on where you encountered it, it usually falls into one of three categories:
A common naming convention used by creators to share large batches of design assets, fonts, or scripts with a community. Dropbox - pack 1522.7z - Simplify your life
If you do download it, use a service like VirusTotal to scan the .7z file before extracting its contents. Dropbox - pack 1522.7z - Simplify your life
If your goal is true simplification, you don't need a mystery "pack." You can use Dropbox's built-in features: Dropbox - pack 1522.7z - Simplify your life