The big problem with 15mph in my opinion is it doesn't allow you to keep up with traffic in 20mph zones. Whole swathes of London are 20mph, if you're going at 1

The big problem with 15mph in my opinion is it doesn't allow you to keep up with traffic in 20mph zones. Whole swathes of London are 20mph, if you're going at 15mph it means you're going to get overtaken in roads which are not suitable for overtaking, and that is much more dangerous than travelling with traffic flow at the speed limit. Perhaps in reality the bike helps you to speed up to 15mph, then you as a rider can take over, but these bikes end up being very heavy. In my opinion it would be much more sensible to have a speed limit in bike lanes which applies to all cyclists (people travelling on normal bikes at 35mph is dangerous in a narrow lane, alongside people pootling along at 10mph), and then a higher limit for e-bikes, perhaps almost exactly 20mph, or 30 kph.