Not sure if this will help you.

Some women may find it difficult or impossible to orgasm through vaginal penetration alone. It is neither a fault on her part nor one on yours. It just happens to be the way things are. The best advice that I can give you is if she says that you are pleasing her then take it as an honesty. But if you are still wanting that orgasm from her you could always try clitoral stimulation during sex. You could use either fingers or even a vibrator to help things along so to speak.

Also, I would like to state that I rarely can orgasm from vaginal penetration alone yet I still very much enjoy sexual intercourse with my partners.

She's "used to much larger?" Than 7"? What? A vaginal canal is only 7" long, and that's only when aroused. When not aroused, it's much shorter, so you shouldn't even worry about that because it's not an issue. I mean, I can't speak for her, but it really is unlikely that it's length. Because if a vaginal canal is on average, about 7" long, then a penis longer than that has nowhere to go. You see what I'm saying? Part of the base will not be able to go in. Anyways, the average size length of a penis is usually never the problem for a female. It's about movement, where it's hitting, how quickly or hard or soft, whatever she prefers.

Have you tried stimulating her g-spot or perhaps cervix, only if she likes cervical stimulation of course? You could try for those orgasms -- x-orgasm (cervical) and g-spot orgasm. It can happen during intercourse if you're trying to aim there.

Even if she is "used to much larger," you shouldn't start focusing on the length being an issue because it's surely not.

Then there's the chance that she just doesn't orgasm internally. There are plenty of women who don't. So you are able to give her clitoral orgasms?

Usually, a common reason for us not being able to orgasm during sex is not being comfortable. Could that be it? If so, eventually, she could warm up. Do you guys have plenty of foreplay first? For most women, an orgasm during intercourse won't happen if there was no foreplay. It's only painful on most occasions if there's no foreplay.

As far as "slaying her like no one else," I do not quite know what slaying is.

You'd really be much better off asking her. It would seriously get you really far. We can offer up suggestions based on our likes, but every girl is so very different that you'd definitely get better results just asking her and then experimenting, letting her find what works for her. That was what did it for me -- taking my time and experimenting, and my partner helping me experiment.

Also, I don't think it's the timing, either. 15 minutes is pretty good. I don't know about other girls, but I usually get done in less than that. It can be a pain though because I want to be able to handle it longer for my own partner, but for me, I have multiples then, after a long while it becomes really uncomfortable and often painful. Sometimes 20 minutes is just fine and other times, 20 minutes becomes painful. 10 is always pleasant though.

No, the clitoral orgasm should not make it more difficult for a vaginal orgasm to occur. If anything, it's the opposite. I don't know a single woman who doesn't orgasm better after a clitoral orgasm. Some can't even orgasm without clitoral stimulation first or during.

Have you guys tried different positions. For now, I'd seriously focus on movement and pace. It's unlikely those other things like size and all are the issue. Like I said, it could be that she just can't orgasm like that, but that does not mean it's impossible! So don't give up. It can be frustrating. For both parties. When it takes me a long time to get there, I get worried and frustrated because I don't want my partner to have to keep doing things for me only, so that alone can stop it from happening -- stress, frustration and worry.

You could also focus on the g-spot during foreplay too. That could surely be a huge help.

there are prolonging creams. also it is very hard to have a vaginal orgasm.