Well, for anyone that might run across the same issue. I know my problem is a larger ruleset for the interfaces on Suricata, so when I try to rebuild multiple interfaces it pushed PHP over the arbitrary 512G memory limit. I found a solution from others with log sizes causing their problem and a solution listed above to increase memory.
I wasn't thinking, so their solution didn't work for me because I was changing the wrong .inc file. My error was for /usr/local/pkg/suricata/suricata.inc and not /etc/inc/config.inc, which is why it wasn't acting like it increased the memory limit. Once I changed the 512M in suricata.inc to 1024M, I was able to rebuild all of the interfaces at the same time without the error triggering.
This is probably more of a "hack" solution, but I don't want to modify my SID management files just to fit the memory when I have more than enough memory to spare and it isn't taking that much extra for Suricata to go from 512M to 1G. One thing to note for anyone trying this is to make sure to write a script or a cron job to sed the suricata.inc periodically in case there was a package update that overwrote the system. Here is my cron job:
sed -i'.inc' -e 's/ini_set("memory_limit", "512M");/ini_set("memory_limit", "1024M");/g' /usr/local/pkg/suricata/suricata.inc
This seems to have solved my issue, but I'll keep an eye out and modify this response in case it occurs again under the same circumstances.