Yikes!! That would require 60 mice per group for 5 biological replicates. Review boards would probably require a lot of justification for using that many animals in each group for just one experiment.
What I have noticed over the last 20 years is that power analyses are absolutely required as part of any grant application or IRB approval policy. I think this is a really good development since it requires scientists to think through their experimental design, hypotheses, and overall model.