>A computer with 64 GB of memory is 4 times more likely to encounter memory errors than one with 16 GB of memory.

No. Or well, not exactly. More bits will flip randomly, but if between the two systems only the total installed memory changed, both systems will see the same amount of memory errors, because bit flips on the additional 48 GB will not result in errors, because they will not be used. Memory errors scale with memory used not with memory installed.