If the network is too slow, then people won't use it as you have found out. I haven't had to deal with this situation but I think the solution is obvious, someone needs to maintain a local network version of the library for each office. I'd be willing to bet that it could be done automatically. Directives would need to be put in place to only use content from those libraries and manufacturer's families need to be put through a vetting process so that they can be modified to suit your needs before being used in a project.