The biggest thing influencing the runtime of a simulation is the number of vertices in the tissue tet meshes and the cloth triangle meshes. These simulation mesh vertices are the degrees of freedom that the solver needs to figure out how to move over time. Doubling the number of simulation mesh vertices in the simulation more than doubles the runtime. The “ziva -info” MEL command will print the number of tet-mesh and tri-mesh vertices to the Script Editor.
To make a sim run faster, reduce the number of tets on the sim by increasing zTet.tetSize. Increasing zTet.tetSize 2x generally decreases the number of tet mesh vertices by approximately 8x for tissues that have large filled interior sections; or by approximately 4x for tissues that are shell-like. One can keep the resolution high just where needed by painting the zTet.weights and using surface refinement as described in the Tetrahedal Meshes section.
The simulation mesh for zCloth objects is the Maya mesh used to build it. Reduce this mesh’s resolution, with any remeshing tool, to reduce the runtime.