When working with sources in ScopeBox, performance is related to a few factors: the number of palettes (scopes) you've got running, the resolution of your source, and the power of your Mac.
One option that can dramatically improve performance is enabling source subsampling within the source settings. This is especially useful with 4K sources.
Reducing open palettes at any one time will also greatly increase performance. When working with a YCbCr sources (most sources), adding RGB palettes like the RGB TimeTrace or RGB Parade imposes a substantial amount of CPU load.