Man oh man. You are making so many assumptions here and I think many of them may be wrong.
Assumption #1: Your wife's former lover's 'problem' was that he lasted a long time. She apparently didn't say this, you inferred it. It could be so many other problems: inability to maintain an erection, clumsy or inept or selfish in bed, etc. Why do you assume it was the one thing that you're most insecure about?
Assumption #2: You have PE or PE is a problem. Despite what men may like to think, most women do not prefer hours of pumping. They want to have a loving encounter and be sexually satisfied. You satisfy your wife every time. Has she complained about how she wishes you'd last longer or is this something you are projecting?
Assumption #3: Your wife couldn't possibly be fully satisfied with clitoral orgasms. This is simply not true. Most women only have clitoral orgasms and I assure you they are very satisfying. It's the only kind I had for most of my life and I have had decades of wonderful, satisfying sexual experiences. In the past couple of years I have learned to have vaginal g-spot orgasms and I can tell you: I could have 100 of them and enjoy them very much but I wouldn't be fully satisfied until I had my clitoral
orgasm.
Assumption #4: You can read minds. You can't. I don't recommend you bring up this past lover of your wife's. But you do need to find out what's going on in her mind. Is she really dissatisfied with your endurance? Or is it the normal complacency that comes with 16 years of marriage and the stress of daily life and raising kids? If you're having sex weekly at this stage of the game and both of you are satisfied by the encounters, you're really not doing badly for this stage of the game. I know it seems like forever away, but the kids do grow up and become less dependent. You and your wife will have more and more time to yourselves and eventually they'll be gone and it's party time.
It's great that you want to spice things up with your wife. Really. Too many marriages founder because they concentrate on everything but each other. But please make it about the both of you. Not just you and your personal anguish. She might be dissatisfied. Or she might just be tired, stressed and distracted by things that have nothing to do with your endurance in bed. Find out what she's thinking. Let her know you love her and want her to be happy. Let her know what you want too. (and changing the past can't be one of the things you want - look forward)
It's great that you're venting here rather than just stewing in this any longer. Get it out of your system here where it's relatively safe. Then maybe you can be a little calmer when you talk to your wife.