Adding buffers to VSAM works like CACHE, reduces I/O and increases performance. What kind of buffers depends on VSAM processing, if VSAM is only Read only, (Dynamic or Sequential), READ and WRITE/RE-WRITE etc.
Also best way is to execute STROBE or any other performance management tools your shop has.
STROBE is a performance measurement system that helps you to improve
the performance of application programs by determining where and how time is
spent in an online subsystem or batch processing program.
STROBE can be invoked by TSO STROBE and there is a TUTORIAL to help you around with options.