Yeah I see the same behavior. I don't think i've bothered to sell anything on the test server because performance was never an issue. I always assumed it was due to DB load, but maybe an index was dropped in prod?
I have very large collections on both servers (full loads of a large majority of items) and I see the same lag on both.
Test Build 2.12 makes a huge difference, at ~6700 items it now only takes 20-25% of the previous loading times.