If the repository is on another machine network-latency would probably be the bottleneck.
I would suggest that you try the branch of pull-request #2195 [1]. In my tests the speedup was huge, I got around 1MiB/s with the current restore implementation, compared to nearly maxing the 250Mbit/s connection with 28MiB/s. This was between two different datacenters (OVH Gravelines -> Hetzner Nürnberg).
Even if the repository is on local storage, I would assume that the “out-of-order restorer” is much faster than the very conservative mainline implementation.
A few links that may help you to understand the current state better:
[1] https://github.com/restic/restic/pull/2195
[2] https://github.com/restic/restic/issues/2074
[3] Degraded restore performance (S3 backend)
[4] Slow restoring speed