Instead of waiting for the filter to do its job at full resolution, I thought it'd be better (in some terms) to create a low-res preview that can render much faster and display an approximate result. Which later can be rendered at the regular resolution.
Similar features can be found in After Effects where you can lower the preview resolution down so things go smoother. Results of sliding values around can be seen immediately.
Who knows... maybe there are other methods of rendering that may be just faster than the one there is right now....