Like all Java processes, the VSE will manage the memory it has been allocated, and will request more from the OS to grow the internal heap up to the size specified by the -Xmx value (which may be specified in the vmoptions file).
Once it has the memory, however, it does not release it back to the OS. If garbage collection frees up heap, it is managed as free heap space. This behaviour is that exhibited by Java, and is not specific to DevTest.
If your CPU utilisation is due to workload, then setting the logging to be less verbose may assist. In the logging.properties file, look for the line that reads log4j.rootCategory=INFO,A1, and modify it to be log4j.rootCategory=WARN,A1 . No restart is necessary.
If you are sure that the VSE is occupying the CPU, look into the vse.log after making the above change - you may receive some indication of any issues that need to be addressed from this log file.