Determining if Memory is A Constraint

I’ve got an iMac with 8GB of memory.

From time to time, Mathematica grinds to a halt in performing certain functions. For example, rotating complex Graphics3D[] output, or more recently, an notebook taking forever to reformat itself when it was resized.

I’ve noticed in the Mac’s Activity Monitor that I am frequently up towards 7.8GB of memory used, with the Mathematica app taking up a hefty proportion of this.

Is there any way within Mathematica to determine if a given slowdown is indeed a result of a shortage of memory?