Thanks. I assume it's about 14 3/4 then. I am trying to see if it would fit in between two shelves if I had it on an extendable vesa mount. The shelve is exactly 15 inches.
I measure the height at 14 15/16 inches. Based on your shelf height of 15 inches there would be very little clearance. I would also be concerned that there would not be enough space to adequately ventilate the iMac since it has a ventilation grill that runs along the underside of it screen (right below the apple logo if you're looking at the front of the computer).