Mavericks actually has increased memory usage improvements than the previous OS. The "7.99 GB" used, as ktomais mentioned, is not real. The "wired" memory is the real "active" one. OSX stores (and in some cases compresses) application data in case you accidentally close an app (e.g. accidentally close Chrome whilst reading a newspaper article); thus, the reboot time for the app is quicker than opening it straight from startup. There are some memory cleaning apps out there, but I'm not too keen on them as they have the potential to slow your system down and/or break processes. However, what they do well is indicate a better approximation of memory usage. The 15-19 fps is odd and has happened to me before. Generally, a system reboot fixes it.