[Max 2015] Slow interaction with rigs using sliders embedded in attribute holder

I’m nearing the final stages of completing an auto-rigger script for Max. I’ve been using v2013 throughout most of the project and everything works fine. When testing on v2015 however, interacting with the rig via sliders is incredibly slow and choppy.

In the foot rig, for example, there are all of the standard sliders for heel roll, toe roll etc. Whilst moving the slider from 0 to 1, the viewport does not update in real time and there is a one or two second freeze after the slider value is changed. The rig is linked to the sliders mostly using float expressions, and occasionally a scripted controller when no other options were available. Once the change has finally been made, the rig runs fine with no lag or framerate drops.

Does anyone have any ideas as to what might cause this?