I think it's 9 bricks high on the main wall, a Lego brick is 9.6mm high (excluding studs).
Therefore on each loop, the new "brick" is 9x as high, starting at 9.6mm
So height = 9.6*9^n, where n is the number of times it loops.

The gif is 51 frames long, each frame has a "delay" of 6, the "delay" is 1/100th of a second
so each frame is 60ms long, so the full gif loops once every 3060ms or 3.06 seconds
in 15 minutes, this will loop 900000/3060 times = ~294 times = 9.6*9^294
which is

338508055594017441094756692154797964164152375705921641266824230420374689281245766351807168590497715128027784165184573903103191590136897398614972942785291493882661403040286849592835728392778574302132343693647310147312978433083418532949035401074849407931316974299738767693582823393545

mm high, or

~3.526 × 10^280 bricks.
or
~3.73 × 10^261 lightyears
which is an inconceivably large number.