I have the r12 apps instance which is running in oracle linux 4 update 5 32 bit.
R12 requires at least 4 GB of RAM and with 32-bit OS you can't take advantage of utilizing more memory. If you consider migrating to 64-bit OS, then I believe you would notice improvement in performance.
Frequently Asked Questions: Oracle E-Business Suite Support on x86-64 (Doc ID 343917.1) -- 4. What are the benefits of running Oracle E-Business Suite on x86-64?
If this is for personal use, you may try mdtaylor suggestions in this thread -- https://forums.oracle.com/thread/493428
As pointed out by Hussein, you cant expect to have a better performance with a 4GB RAM utilization by the OS. I suggest you to to migrate to 64bit OS if you have memory greater than 4GB
Please also refer note:
How Determine The Hardware Specification : CPU, DISK, RAM (Memory) For E-Business R12.1.x Installation? (Doc ID 789438.1)
Just to troubleshoot with your issue, try running ADDM report to get a quick review of the current situation. Also ensure you have Gather Schema Statistic program scheduled.
But anyhow, I dont thing you can expect a greater performance boost.
Let us know if there are any further concerns.