I don't know if this is the exact answer to your speed problem, but that article you quoted suggests that you add a new ADO.NET Data Model to the class library containing the RIA Service.
There's absolutely no reason to generate a second data model, as LightSwitch already generates one when you attach the external data source (your SQL Server database). You may as well re-use it. An EF data model takes time to construct, so I suppose that using two EF data models could explain the slowness you're experiencing, but it could also be something else entirely.
Have a look at this article (the original RIA Service/LightSwitch article, & still the best), which among several other techniques, Eric will show you how to re-use the data model that LightSwitch creates for your data source.
How Do I: Display a Chart Built On Aggregated Data
In this article, the RIA service is created to specifically aggregate data to display in a chart, but you can do whatever you need to do in it. It doesn't have to aggregate data. I use RIA services with an attached data source (a SQL database) extensively, to provide data for lists, reports, as well as lookup data for combo boxes.