This is being reported against iClone 7.3

Every time you open the Iray "Preview" window, it puts the model in to VRAM (memory on your graphics card). But it never frees up that memory when you close the Preview window.

The bad result is you consume more and more of your graphics card's VRAM, and can eventually use all of it, at which time you will have horrible, horrible performance.

The only way to free up the memory is to close the iClone entirely.
Starting a new project (without closing iClone) will release the "project" memory but will not release the Iray Preview memory usage.


TO DUPLICATE:
Simply do the Iray "Preview" over and over again, closing the window each time.

My VRAM utilization jumped like this: 2760... 5087... 7089... 7439... 7788...

Here are some additional statistics, gathered by the user "4u2ges." (Thank you.)
GPUZ (Mb) iClone Stats (Gb)
iClone closed 900 -
iClone opened 1520 0.7
Scene loaded 5345 4.6
1st Preview (black window) 7560 6.9
2nd Preview (normal) 11020 8.1
Close Preview 10900 7.9
3rd Preview 11060 7.9


NOTE:
The same behavior was observed on my Win7 desktop and Win10 laptop.

PICTURES:
1) Screenshot of my "GPU-Z" monitoring. Notice the stepped increase in memory usage each time I did an Iray Preview.
2) Only closing iClone entirely will release the memory.