Well, even not plotting the graphic help. But now I think that the problem is with my machine, my operative system or my Mathematica installation, because the same notebook running on Bobby machine takes 3 seconds making a plot like
and 0.5 seconds making the plot
with the "notation" defined in my last email, while in my machine it takes 140 seconds to make the first and 0.5 to make the second. I'm going to try a reinstallation.