We have a WIP potential fix here:
EsotericSoftware/spine-runtimesf05a152

This makes physics very smooth even when physics updates much less often than the render rate. Now it is smooth eg for slow motion (can be simulated with 10% speed in the Playback view) and enables using a lower physics update rate, eg 30fps (now the default) without a noticeable difference in many situations, reducing CPU usage.