Among other possibilities, you might want to memoize that objective. This is done as
StressError[p1_, p2_, p3_, p4_, p5_]:= StressError[p1, p2, p3, p4, p5]=...
Once computed for a particular {p1,...,p5} it will subsequently be found by lookup.
Also it might be useful to define it in such a way that it only evaluates when given
explicit numeric input. If symbolic processing is any part of the speed issue, this
change will redress that.
