That's not a problem with the installer, and surely our the bandwidth is not limited by us in any way.
It's just that, because of the sale we are having AND the O'Hare update we released at the same time, more people are downloading installers now, so the bandwidth we have, which we give out entirely, is shared between more people than usual.
In any case, if you need to install multiple sceneries at time, there's no need to self-update the same files multiple times so, you can do the following:
1) Install any scenery with the NETWORK DISCONNECTED. The installer will detect you don't have an internet connection available, and will ask if you want to continue using Local Files instead. Press the Next button and the installer will proceed without going online.
2) Repeat this for all the sceneries you need to install, always with the network disconnected
3) When you are done with all the sceneries, turn the Network back on, then install the Stand-Alone Addon Manager with the network on, so everything will be updated at once.