Information Loss in a Multirate System
Since in your system there is no aliasing and you do not filter away important parts of the signal (because LP is having the correct cutoff-frequency), there is no information loss. 

When a system changes the signal shape, it does not necessarily mean that information is lost. As long, as the operation is reversible, the same amount of information is contained in $y[l]$ and $x[n]$. However, even though the same information is contained, it can be differently difficult, how to extract the useful information from a given signal, depending on its shape.

However, in reality this ideal low-pass filter does not exist, and it might lose some information.