Which exchange are you on?
Also, switching to ADSL2+ may not get you much greater speeds for a number of reasons (the increase in speed reducing in amount the further away from the exchange you are, congestion at the exchange may now allow any greater throughput than you are currently getting, line quality may not allow faster speeds, the list goes on).
I have even seen people get worse performance after switching from ADSL to ADSL2+. While this may seem counter-intuitive, it can happen. As for the VPN, which software are you using to connect (I realise that this is usualy governed by the company you work for)? I have found that Cisco is by far the worst on lower bandwidth systems, it doesn't seem to cope particularly well.