Hi,
Don't Jump into Parameter tuning initially.
Do your initial & detailed checks of why System hangs.
for example, when System is slow check if you have any work process free or all are occupied, if you are unable to see it from SM50 then check from sapmmc. Check DB relevant things, since you say its Oracle check if Update Optimizer runs regularly. check CPU utilisation, check top contributor for high utilisation etc... and at the end of your analysis you will make out what parameters have to be changed.
Warm Regards
Sujith