Any thunderstorms around last night?
On FTTC, as well as interleaving lowering the connection speed it does strangely always raise the maximum attainable.
Do you know whether you are on an Huawei cabinet or an ECI
If it's ECI I'm not sure what might happen next. Possibly the interleaving will be removed in a while. On Huawei I think it likely that G.INP will be activated within three days. That will leave you with a small level of interleaving and return your latency to what it was before, as well as adjusting the connection and attainable speeds to normal.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 63679/13080Kbps @ 600m. BQMs - IPv4