a higher snrm would no doubt reduce the errors but would it stop them, my guess no.
When I had a really high error rate adsl line I Could control my snrm with my router and I started playing around with it one day, even at 30db it had errors but were at a very low rate, that low rate turned to moderate at about 22db snrm, and anything in the mid teens or lower had a high rate of errors although not high enough to be service affecting.
On my US on my new pair on FTTC, the errors are way better than my previous pair (about 10%), and it has a 12.4 db snrm and still got some crc errors but very low, only 13 in 31 hours.
FEC is always higher than the equivalent CRC so if e.g. a fast path line with say 4000 CRC a day moves to interleaving, it wont get 4000 FEC a day it isnt one FEC to one CRC, the multiple is much higher, as I think when FEC makes a correction it does the entire block of data and the whole block is counted as FEC's. This is why people who might have noisy lines can see FEC in the millions as its an inflated figure.
20k a min is definitely high tho, a line where interleaving is probably saving him from a service affecting error rate.