This answer claims that $ LL \subseteq LR \left( 1 \right )$ where $LL = \bigcup_k LL(k)$.
But is this true? Is this grammar a valid counterexample?
$ S \rightarrow a | Aaa $, $ A \rightarrow \varepsilon $
It's easy to show that this grammar is not $LR \left( 1 \right )$, but I think that it is in $LL(2)$ - the longest string that can be derived is two letters so a lookahead of two tokens should be sufficient.