Renders are taking too long.

Repetile can use a huge amount of memory, and mixing it with an expression and Time Displacement most certainly disqualifies this as a simple composition. Visually, it might not be that fancy looking, but you're asking AE to do a lot. Instead of using Repetile, I would try copying and pasting the comp and using expressions to automatically offset the position of each comp based on the previous index's position. This will save you the time of having to manually position each copy. This should only take a few minutes to setup a test to see if it render faster than Repetile.

You should also check out the new Composition Profiler to see where you botttlenecks are. This is exactly the kind of situation where this tool shines: https://helpx.adobe.com/after-effects/using/composition-profiler.html

Be sure to read the documentation to clearly understand how to intepret the results. Pay special attention to render times with an asterisk next to them as those numbers are being calculated with pre-cached information, i.e. something might read as 5ms to render, but that could be because it already spent a long time caching the object in the first place.