Hey - thanks for letting us know. This is something we're aware of and are trying to replicate - we'll keep you updated when we have a fix in place (hopefully sooner, rather than later!).
In the meantime, try deleting your cache (jcache files inside C://ProgramData/Jagex/RuneScape) and let us know if that works.
EDIT: More information:
The only players who should be deleting the cache are those that have ran the installer recently, be that a re-install or a regular install, as any players experiencing slow loading will have their issue exacerbated by re-installing the game.
Also note this cache issue is Windows only.