7.2 GB does not seem large to me. Not sure if adding an additional Journal Vault Store is necessary. How many millions on items do you have in the existing Journal Vault Store?
Make sure you or your SQL dba is running SQL 'maintenance' on the databases regularly.
i.e. backups, transaction logs truncated, 'SQL' index rebuilds, updating statistics, etc. are all part of normal SQL hygiene... 'SQL' index rebuilds (not EV indexes) and updating statistics are especially important if you have have added/remove a lot of data recently or recently moved the databases.
How to Automatically Backup and Perform Recommended Maintenance for Enterprise Vault (EV), Compliance Accelerator (CA), and Discovery Accelerator (DA) SQL databases
The title of the first item may seem misleading… it has the SQL index rebuild and update statistics commands that I mentioned above. The second one explains how to move the databases and the third one has super detailed steps on SQL maintenance for EV databases.
If you don't have a SQL dba to work with on this and/or you are not comfortable with any of this then please also consider contacting our technical support group for assistance. There could also be something else going on with your SQL environment causing the perceived slowness you mentioned above.
As Rick says 7.2GB VS DB is nothing..... Instead of working around an issue, I would speak to support and resolve this issue instead of createing a new VS and running into this problem again in the future.