For multiple executions use the ‘performance commands’.
Is it a documentation session?
if you have a script that is running multiple blcli commands in sequence the performance commands will speed it up (https://docs.bmc.com/docs/display/bsa86/NSH+performance+commands?src=search) because it won't do the jvm spin up, connection to appserver, authentication, command run, disconnect, jvm close for every command.
for a single command execution there's not much you can do i think. 30s does seem a bit long though. what os is this, and is this running on the appserver ? a client system some where (w/ what connectivity to the appserver) ?