Assuming that you are not experiencing any loss of throughput, then I would think there will be no problem with a DS SNR dropping to around 5 dB.
(Some years ago, when I was experimenting with an HG612 as a modem/router on my ADSL2 circuit, there was one evening when I was subjected to prolonged RFI. The DS SNR dropped from the target margin of 6 dB and slowly fell to -1.9 dB. (Yes, minus, as the "noise" was "louder" than the wanted signal.) The throughput decreased as the SNR decreased. By the time the SNR reached 0 dB there was virtually no usable throughput.)