There is no reason to switch all lines to interleaved. For a co-op term, while I was away from home, I got DSL just for fun because I'm a cable fan. I was 5.1 km from the exchange and they had me on a 1 Mb connection (standard is 3 Mb). However, I just couldn't browse, and max throughput I got was like 2 kb/sec. The reason for that was because of my distance and noise in the poor wiring of the house. After calling tech support, they offered to run a few tests, and I can then pick one I want.
The first one was a 1 Mb fast path connection (which I complained about). Poor quality.
Next was a 512 Kb fast path connection, which was better, but still high rate of packets being dropped.
Next, he bumped me to 1.5 Mb interleaved. Latency increased, but much better performance, but still not reliable enough.
Lastly, and this is the one I picked before canceling the service, was 1 Mb interleaved. It worked, but was too slow for me (I am used to much faster).
This was all done over a period of about 30 minutes on the phone. According to the techie, they only use interleave when the customer has a poor line, and/or is far far away from the exchange. Interleave is slower and has a higher latency, but can more readily deal with line noise and poor signal strengh (due to distance).
What Telkom doing is obviously not in your best interests. They're up to something.