You are underpowered across the board; even the sound system is being bogged down.
Part of the trouble is that Archives needs a lot of clean-up. A little was done before release but it's still a beast that needs performance work. That's why Static Prop and Other Model is so large. It beats up my FPS, too.
World Rendering may be your video card, but since Sound is huge, too, I'm thinking these subsystems are really just waiting around on the CPU to attend to them
Before you go hard-core on dropping your video quality, just try dropping to the low options in the menu and run at 640x480, or even 320x240. If the improvement is small, then you know it's your CPU that's at fault.
I hate calling a Celeron a "CPU," doing so is disrepectful to non-hobbled chips.
Beyond that, read your Whisper, he is a quality information source.