Due to the encryption, hashing, and compression performance can vary greatly depending on hardware and settings. A large number of files can also affect the .sqlite database performance.
There are some hashing improvements in the testing stage and starting with 2.0.2.8 canary there’s an improved hashing function that might help.
You can also try reducing your compression level with --zip-compression-level=1 (or even 0). Choosing an appropriate compression format can help as well (for example, zip is generally less taxing than 7z).
The database functionality is slowly being reviewed but so far nothing major has been improved in the backup job process (but there are some great advances in restore performance).
Removing compression and changing the hash algorithm sped things up for this user by 33% and 15% respectively…