Workbench uses Samres data for post-processing. I would strongly recommend you to contact your local support. Our teams have experience with this kind of transition and will be able to assist you.
This is indeed surprising, as the opposite would be expected with R16 - feel free to join our webinar about R16 on Wednesday, there is a portion on contact that will show advances in performance. See https://marketing.ansys.com/rc/ansysinc/tp/15070
For your current probleme, I would recommend...