Try to use the version 5. It's lighter on resources than 4.8.
But, I think it will be a matter of having/installing more RAM and not disabling the antivirus.
You can test other antivirus, but I really don't think you'll get it better. Also, do NOT forget that the RAM displayed on the task manager does not take into account the driver memory usage. AVG and Avira, for instance, loads kernel drivers (which take RAM) to perform the protection. This RAM is NOT shown in task manager.