Thermal motion promotes lateral position exchanges between lipid moleculaes within a monolayer. In an artificial bilayer of lipids, this movement has been estimated to be ~ 2 um/second. On average, do you expect the lateral movement of a lipid molecule within a biological membrane to be equally fast?

No, the lateral movement of a lipid molecule within a biological membrane will not be equally fast as the movement of lipid molecule in a artificial lipid bilayer.

Explanation:

The artificial bilayers are taken as a model to study the biological bilayer in laboratories.The artificial bilayers  differ greatly in composition from the true bilayers.The artificial bilayers are mostly made up of phospholipids and very less amount of sphingolipids. It lacks the integral protein and other molecules.The Biological membranes have integrated proteins and other molecules within the layer.These molecules offer resistance to the  movement of lipids  in the membranes. So, the speed of lipids in biological membrane cannot equally fast as their speed in artificial bilayer.