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Increasing the number of rows per batch is actually the only thing you can do to speed up the backup. Akeeba Backup sets the PHP memory limit to 1 GiB. If you have the available physical memory (i.e. your server won't start swap-thrashing) increasing this value will try to load a lot of the table being backed up into memory. Don't worry about setting this too high; Akeeba Backup checks the average row length, the available PHP memory, and applies a conservative scaling factor to reduce the batch size if necessary. We created this protection and made sure it works in the real world out there before allowing you to increase the batch size to very high numbers. If I recall correctly, the maximum limit we've set is a million rows.

Beyond that, it's just down to the CPU single-core performance and the I/O throughput of the server's storage. Remember that server-grade CPUs tend to have loads of cores with relatively weak single-core performance each. So, of course, the speed at which data can be read, compressed, and written to the archive will be lower than on a desktop (and most high-end laptops, to be honest).