Where were you downloading from? I'd try downloading the ISO from a different location and see if the speed is better. If you really want to check further then run a traceroute from yourself to the download location and see what the times look like. Network topography and server bandwidth are the most likely reasons for slow downloading.
+1. You'll need to install traceroute from Synaptic. After doing so, open a terminal, as normal user, do:
/usr/sbin/traceroute google.com
Google is just an example. If your download source was ibiblio, for example, it would be:
/usr/sbin/traceroute ibiblio.org
No need to type the whole path
/usr/sbin/traceroute ibiblio.orgit works just fine this way
traceroute ibiblio.org[dwmoar@laptop ~]$ traceroute ibiblio.org
traceroute to ibiblio.org (152.19.134.40), 30 hops max, 60 byte packets
1 192.168.10.1 (192.168.10.1) 2.052 ms 3.011 ms 3.804 ms
2 192.168.1.1 (192.168.1.1) 11.344 ms 11.959 ms 12.293 ms
3 * * 66-112-77-217.stat.centurytel.net (66.112.77.217) 14.151 ms
4 rb2-bras.aur.centurytel.net (69.29.185.51) 16.904 ms 18.358 ms 19.846 ms
5 aurrorcoro2.aurrorcoro1.centurytel.net (209.206.179.130) 21.671 ms 22.754 ms 24.165 ms
6 host.lightcore.net (208.110.249.218) 30.318 ms 15.888 ms 52.469 ms
7 bb-sttlwawb-jx4-02-ae0.core.lightcore.net (206.51.69.142) 16.191 ms 17.315 ms 18.462 ms
8 sea-edge-12.inet.qwest.net (67.132.130.213) 20.647 ms 23.179 ms 25.175 ms
9 chr-edge-03.inet.qwest.net (67.14.35.46) 99.074 ms 108.046 ms 108.322 ms