You can try e.g. TM_RdaemongetCompletionList('q')
Hmm… I've reinstalled R to 2.14.1 and it works it works quick as expected.
Maybe also I got wrong impression it's slow, but it just tends to jam in TM2. i.e.:
(1) type plot( (2) press ^,
Parameters popup menu won't appear until you press other key.
Also ^. keeps working weird if: (1) type plot (2) press ^. (3) delete everything with ⌫ (delete) (4) "plot" autocompletion reappears, but there's no word at all
Only the first invocation could be a bit slower if the TM R helper daemon does not yet run.
It is pretty amazing contraption, I guess it is most advanced completion of all TM bundles.
Cheers,