This is perfectly normal. 2GB of memory usage for a game client is really very little these days.
The reason that it increases during play is that Turbine disabled the loading of certain game information during loading to reduce load times and, during play, you may invoke the loading of that information which is then permanently stored in memory until you exit the client.
[center][url=http://forums.lotro.com/showthread.php?18699-How-to-get-help-on-the-Tech-Forums-and-how-to-contact-Turbine][color=gold]How to get help on the Tech Forums and how to contact Turbine[/color][/url]
[color=green]Please reply to the topic or PM me if a solution I posted works for you: The more data I can gather the better I can help.[/color][/center]