Well, as far as I know, the only thing that works for pe is kegel exercises.
I am not worried about pe, but when I was, I recall these exercises helped a lot.
Try them for a month everyday (get more info on the web for actual exercise), and see if it makes a difference.
The reason you last so long the second time is obvious. There is hardly anything left to come out.
If your wife tires out after the first "round", then you can masturbate solo first and then start with her so she is fresh to begin with.
Good luck to you.