|>> But can't these kinds of LAN's also be used to get very fast download speeds from the rest of the Internet? <<|
No. The normal LAN speed is 100Mbps. The fastest Internet speed you are likely to get is 8Mbps and that is all you will get, regardless of what speed the LAN is capable of. You are only as fast as the weakest link in the chain and the weakest link is between you and your ISP.
The 1.5 Mbps is not fast, unless you mean Bytes per second which is about normal for a heavily loaded LAN. Data transfere speeds are usually measured in bits per second. If you mean 1.5 Mega bits per second that that is very slow, even for a home network.
Though a LAN may be capable of 100 Mbps, the is no absolute guarantee that you will get that speed. There are other factors to consider, not least of all in a coprate network is how many other people are using the network.
I think Mr Bloom, you need to buy a book on networking and learn some of the basic principles. Paying £50 for a network service is silly unless you are running a very large company.
A home network can be set up for less than £100 with no on-going costs except for your Internet connection which is nowhere near £50 a month.