Your memory limits need to be the same on your development/staging environment as on your live site - otherwise a script which works on one, will not work on another.
So reducing any memory allocations would not be wise.
If you are using the same server for both development and production stores - separation via VPS seems a little peculiar (if you are trying to keep memory overheads to a minimum) as you will encourage additional RAM usage simply to run a duplicate of every service?
It would make more sense to run your staging site on the same VPS as your production store, running the PHP instance as another user that has specific limits set in
/etc/security/limits.conf - then you can prevent runaway memory usage, number of processes and anything else.
If you truly need resource and platform separation (ie. for PCI DSS compliance or even just best practice), then in your staging/dev VPS, simply set a maximum of 1 Apache thread. If you are the sole developer, there will only need to be one process/spawn running.
RAM is exceptionally cheap - just buy more. Don't constrain your application or try to run twice as much with half what you should have.