mgpaddle, you're asking a question that's outside the scope of this thread. I'll answer as best I can, but if you have any other questions about it or want some background, you should start a new thread.
An iPhone will allow the same choices for any of the main e-mail protocols in general use today, POP3, IMAP, and Exchange. (There are others, but I don't know anything about them.) Exchange is Microsoft technology that involves a heap more data than just e-mail. POP3 is e-mail only, a standard technology, that pulls down messages to your e-mail client and off the server (unless you specifically enable them to be left on the server). IMAP is e-mail only (I think), a standard technology, that keeps messages on the server but allows you to download the headers or the full messages, depending on how you configure it; it's good for multiple devices.
With any of those, you can set up an iPhone so that the messages get pushed immediately to your phone; or so they are fetched on a frequency you establish; or so they are available only when you go into the Mail app. All of those settings are in Settings/Mail, Calendar, Contacts/Fetch New Data.
The web is probably chock full of advice on how to set those up. Be aware, though, that the biggest consequence of different configurations is battery-related. If you fetch frequently, your battery will drain more than if you fetch manually. If waiting fifteen minutes is too long, then you probably don't want any fetching--you want them to be pushed.