Unfortunately it is not possible to determine if and how this causes problems with OpenVAS or redis based on this information alone. You can create an issue at Issues · greenbone/openvas-scanner · GitHub, maybe you can exchange the required information with our developers there.
We cannot give any guarantee that this is solveable with the current generation of OpenVAS, however. But we are currently working on the next generation which should hopefully address such problems.
For further performance tuning you can also check the man page of openvas regarding the configuration file options min_free_mem, max_hosts, max_checks, and the man page of ospd-openvas for the configuration file options min_free_mem_scan_queue, max_scans, max_queued_scans and scaninfo_store_time.
Last but not least, with our commercial solution it may also be possible to distribute the scan load by employing sensor appliances.