The timing is set -T4.
If I scan manually to same target it takes 87 sec instead of 15-30 min with openvas. I also use -p- for the scan so all 65k ports.
I have one nmap that takes 1 hour and 10 min now. I found this Optimal timeout setting for OpenVAS - #2 by cfi and deciced to change unscanned_closed_udp and set it to no.
I also changed the IANA rule to nmap all tcp and top 100 udp. Saving lots of udp ports.