1. As I.Am.The.End stated, lasting too long can be worse than not "long enough". I put that in quotes because there are plenty ways around your problem. You don't have to penetrate for 15 straight minutes. Learn to use all the different parts of your body *wink, wink* and your partner will be far more satisfied than if you just pump away forever.
2. Yes, it's good to "purge the system". It helps to "milk" the prostate regularly and it's believed to actually help lower your chances to develop prostate cancer. I'm not saying you should beat it like it owes you money, but sex/masturbation does help with prostate health.
Frequent Ejaculation May Ward Off Prostate Cancer

In conclusion, having a shorter build-up period doesn't make you less of a man nor is it the key to satisfying your partner. Learn about your self, use your brain more and stay in tune with her and you'll both be more satisfied. And yes, the poison must be purged!