That’s a long-outstanding one we see regularly in the Bug Report / US Technical Support forum and the workaround for that is…
Options > Video > Quality > Texture Quality
Whichever setting this is set to, set it to the other one, apply the change, set it back to the original option, apply the change. This should resolve the slow display of inventory items / blacksmith stuff / kadala stuff for that game session. You may have to re-do this each game session. No known permanent solution, unfortunately.