Its can be normal for
SNR to fluctuate a bit.. but it depends on how much its fluctuating and and if theres a pattern to it.
routerstats is a good tool for being able to record your SNRm and it will do all the hard work for you, by taking regular snapshots of stats from your router and outputting it as a graph.
Results from a routerstat graph can often be quite telling as whats going on on your line. Its one of the tools we use most to help troubleshoot problematic lines.
>> Is it possible that i could be experiencing gaming online issues because my upstream is suffering from crosstalk at the exchange?
This doesnt sound like crosstalk.. its impossible to say without seeing whats happening to your SNR.. but its probably more likely to be internal wiring,
EMI/REIN or a line fault. Crosstalk doesnt cause SNRM's of 12-15dBm