Please see (How Determine The Hardware Specification : CPU, DISK, RAM (Memory) For E-Business R12.1.x Installation? (Doc ID 789438.1)).
R12 requires at least 4 GB of RAM. The total space required for a standard system (not including the stage area) is 85 GB for a fresh install with a production database, and 233 GB for a fresh install with a Vision Demo database. You will need at least 47 GB to accommodate the file system and database files in the stage area directory.
Please also see previous threads which discuss the same topic.
4 GB is what you need for R12 only, and your OS would also require at least 2-4 GB of RAM. If you are low on memory, please see some tips and recommendations in this thread -- https://forums.oracle.com/thread/493428
If you still have performance issues, then you may need to consider adding more memory.