From your stats it looks like your sync speed is 22Mbps which, as you say, is what TalkTalk predicted so all looks good there. What is your actual throughput speed (i.e. as measured by a speed test website)?
As for the increased latency, it looks like the DLM has applied interleaving to your line (hence the non-zero FEC count) which does increase latency. This does happen when the DLM is reset, but usually is taken off after a few days. Then again, your FEC count seems very high for just 10 hour of uptime. FECs are effectively 'errors that didn't happen', as the interleaving has corrected them, however if interleaving was off these would likely be a large number of CRCs which likely would effect your throughput speed. It looks like the DLM is doing its job here, and keeping interleaving on to keep your line stable. The question is why is this necessary? Can you hear any noise on the line if you use a corded phone plugged into the test socket?