With your sort of connection speed, in favourable conditions you should be able to download 1 MB in a couple of seconds or so. Say about 1 minute for 18.7 MB. If you were getting about one tenth of that speed it could be due to:-
- a slow server
- traffic management by your ISP
- congestion in your local exchange or at your ISP
- poor configuration of your own equipment
You can't do anything about the first three, but it might be worth checking out your MTU and RWIN values, see
here.It's unlikely (I think) to be a problem with your wireless connection, unless you're operating at the extreme of its range.