It's better not to think of tests as having high algorithmic complexity, but rather code itself.
Look for areas of your code where the NCrunch hotspots are showing your tests as spending a large amount of time, and suppress coverage for these areas. These areas are unlikely to cover a very large part of your codebase.
Alternatively, you can turn off the
analyse line execution times setting. This will turn off the tracking of performance (hotspots) and will reduce the weight of instrumentation. Impact detection will not be affected by this change.