A few things to keep in mind, however...
- All memory is virtual. The amount of virtual memory allocated to a process has no direct bearing on how much physical RAM is being used.
- If there is no competition for memory being manifested at this time, i.e. physical memory supply is adequate and there's not too much going on, then the computer will be quite "lazy" about cleaning-up the memory used by a particular process ... hey, he used it once, he might use it again! Why bother if nobody's complaining? Indeed.
time when the "memory use" of a process might really make a difference is when the system is persistently and actively swapping,
because there is not enough memory to satisfy the demand and
this condition has been going on for several minutes or more and
processes, which weren't "just started-up moments ago," are actually being human-noticeably delayed by it.