The slow speed sounds like some sort of hard drive speed issue to me, but I'm probably wrong.
Regardless, here's a few ways to speed up your internet speeds.
1) Use a download manager that supports pausing and resuming downloads. This allows you to resume a "broken" download on most servers. My favorite download manager for Windows is Flashget 1.9. I don't particularly like the new version (3.5), but you might want to try that as well.
FlashGet(快车)-Best Download Manager
2) Make sure that your download manager knows to use multiple connections. This simply causes the download manager to download multiple parts of the same file at the same time. It can speed up certain connections. This is automatically enabled in most download managers.
From what I've seen, USB 2.0 speeds when not using a system cache tend to average around 22-25 MB/s on my computer. In other words, you should be able to transfer a 1GB file in a bit less than a minute. Extrapolating onwards, you'll have over 60 GB in an hour and so on.
Downloads using a 10/2 internet connection such as your own should average to around 1.25 MB/s. In other words you should be able to download about 75MB a minute and 4.5 GB an hour. 150GB will take about 33 hours to download. If your download said 15 hours, you're downloading at approximately 2.5MB/s.
Keep in mind that your rated line speed is measured in Megabits per second and your actual download speed that you see is rated in Megabytes per second.
As a last note, you should know that most online file backup solution tend to have low download speeds. This is the one part of these services that tends to suck. While it's a great place to store your files in case of file loss, when you want to download the backups it will take much longer to download them than it would if you used a commercial file storage solution such as Rapidshare, Megaupload, Filefactory or Hotfile.
More info on the speeds and math involved:
Line Speeds from your ISP are rated in bits.
The download speed you see in your download manager/browser is rated in bytes.
There are 8 bits in a byte.
To learn how long it will take to download something:
First take your line speed (10/2) and convert the first number (10) from megabytes to megabits. To do this, simply divide that number by 8.
10 / 8 = 1.25 Megabytes/second
Once you have your download speed in megabytes, divide the total size of the file (in megabytes) by that number. If downloading a 143 GB file:
143,000 / 1.25 = 114,400 seconds
That number is the number of seconds it will take to download the file, divide it by 60 to get minutes and so on if you need hours.
114400 / 60 = 1906 minutes
1906 / 60 = 31.7 hours
This gives you a final answer of approximately 31.7 hours to download the 143GB file using a 10/2 line. This is approximate due to the fact that there are actually 1024 Megabytes in a Gigabyte (Dividing by 1000 is easier) and line speeds tend to vary more than they are constant.
As a general approximation, you can divide or multiply each level of bits and bytes by 1000 to get to the next level, the actual number is nearer to 1024.
~1000 Bytes in a Kilobyte
~1000 Kilobytes in a Megabyte
~1000 Megabytes in a Gigabyte
~1000 Gigabytes in a Terabyte
and so on...