Hello James,
Performance issue could emanate from various reasons,
It could OS, DB or SAP, first we need to understand and evaluate where could be the issue.
If the SAP system old and probably bigger database size then you should consider Reorganizing DB.
I could see from your inputs the from SAP you have provided better SWAP space. Assuming OS working fine(most of the time) you can focus on reorganizing and re-indexing on DB side.
Best option would be to check SAP early watch alert report for pointers first before doing anything.
Regards
Anand