Simple things first. I think LWP pulls the response into memory. 23Mbyte isn't that much, but is there a chance that your windows box is working near the limit of it's RAM? (Check the 'commit change' in task manager - if its close to your physical RAM then you probably are close to paging).

If so, you could simply be seeing paging activity account for the difference.

Other than that, can you try other methods? Perhaps the network to your windows box is congested?

Does your web browser take a similar length of time to fetch the file?

It still could be LWP, but it would be useful if you could check the windows box is able to fetch the 23Mbyte quickly using other methods.