this is almost impossible to answer....
because the levels are somewhat tied to the style of music,
and how close your final mix is, to how you want it to sound,
and how good your mix actually is.
if you do not need to do any more compression, leveling, boosting, ANYTHING that would be required to properly master your songs, then you are probably ok with those levels...
but if you have any question at all,
i'd bring those peaks down to closer to -10 to -6,
and RMS of 18-22 isn't a bad place to be.
there is NOTHING to be gained by mixing hotter.