As long as the connections are not slowpath/F2F, they can be forced to the fastpath: sk156672: SecureXL Fast Accelerator (fw fast_accel) for R80.20 and above which will be substantially more efficient.
Keep in mind however that doing this will disable all deep inspection on this traffic (including HTTPS Inspection if active), so if a virus/malware tries to propagate through these connections it will be allowed through with no logging.
To diagnose if these connections are in the slowpath (in which case trying to use a fast_accel will simply not work) run this command and search for the connections in question:
fw tab -t connections -u -z
The new -z option will only display connections in F2F/slowpath, and also why they are stuck there ("reason") for R81+.
Gateway Performance Optimization R81.20 Course
now available at maxpowerfirewalls.com