Running Collect periodically probably won't help much in this scenario - the huge data structure isn't actually being collected during the GC.Collect. But the GC doesn't know this until it spikes the CPU while it walks a bajillion references.

Since nothing is actually getting collected, if you ran GC.Collect periodically, you would just be incurring more lag with no benefit. I think your idea might help more in a different situation, one where you do have large amounts of memory getting reclaimed with each GC sweep.