RAM usage seems to vary, at least in my cases, here is my data of increased RAM usage after customizing IPS rules, and checking “Threatfox IPS Rules” and hitting APPLY,
APU2 - 4GB RAM -AMD- Jaguar - RAM usage increased 2GB
old desktop #1 - 4GB RAM - Intel i3 - RAM usage increased 1.3 GB
old desktop #2 - 8GB RAM - Intel i5 - RAM usage increased 0.7GB
Looks like available the RAM usage increase is negatively correlated to available RAM
There might be other factors than hardware but I thought it is interesting to list.
I wonder if Kernel versions have an effect besides the CPU and total RAM available