I’m confused. It shows iMac17,1 which is the current model, but the current model is Retina display only, but your screen size indicates it’s not retina?
That said - while you got the latest iMac, it appears that you got it with the lowest available specs in terms of RAM, Processor and graphics processor, and the reality is that is going to make life difficult with something as intensive as 3d design… especially the 8GB ram. I run an i7 iMac with 32GB and I sometimes have memory issues when running Rhino (Granted I also have Safari, Photoshop, Quickbooks, Mail and usually a few other apps open at the same time). I suspect if you max out the RAM you’ll see a big improvement. Also not addressed in your specs is your hard drive. In theory solid state or Fusion drive should give better performance.