Geometry quite often is the problem…
particularly overly detailed entourage like furnishings or landscape items…
Goldilocks can check LOD of geometry or textures…
if a big model performs OK in ‘Monochrome’, ‘Color by Layer’ or ‘Shaded’, but lags in ‘Shaded with Textures’ then it is more likely to be textures…
turn off ‘Use maximum texture size’ as an initial check…
if it lags in all, it is most likely geometry, both and/or Extensions…
the more things that want to auto update after every change the slower any model will perform…
so close ‘Outliner’, ‘Material browser’, ‘Scenes [with Thumbnails]’ , ‘Layers Panel’ , and ‘Components’…
turn off or remove all renderers unless your rendering…
un-croped screen grabs of kitchen appliances is the worst case I’ve seen lately…
john