There's many "easy" ways. If by "easy" you mean "not a lot of time needed," however, which is what I find most people really mean, then you're out of luck.
Unfortunately, you're not going to make gil unless you stop levelling, and spend solid hours doing something just for the money. This is the biggest conceptual obstacle I think a lot of newer players have: they're proceeding along in level 7 equipment at level 30, and complain that they can't make enough money when people tell them to upgrade.
You've just got to put the brakes on your levelling for a bit, and do nothing but money-grubbing for a while.
Of course, you're level 15, on your first job. You don't really need a large sum of gil yet, and nobody's going to expect you to have it. Once you're around level 20, and are thinking about doing things like obtaining your chocobo license, and levelling your first subjob, then I'd worry a little more about it.
The money-making method that is most favored by newer players is farming. That means you go out, kill a lot of lower level monsters, and sell the drops. You'll want to target things with highly-sought after rewards ... bees for beehive chips, crawlers for silk thread ... that kind of thing. Have a target.
I'm not sure about current prices, but you can make roughly 8k - 15k selling a stack of beehive chips, which are very easy to get, or from 30k - 50k a stack on silk thread, which are a bit harder.
I'd also recommend investing in a fishing rod, heading out to San d'Oria or Windurst, buying a few stacks of little worms, and sitting down for a while to catch moat carps. These are still a very good source of income, for a lower-level player. They're always in demand, as they're required for the Lu Shang's quest, and they sell very quickly. I've seen these things go for anywhere from 8k - 15k a stack recently.
The key word here, is TIME. There's absolutely no reason for you to be "poor." It all depends on how much of your playtime you're willing to invest making yourself wealthier.
EDIT: I also couldn't help but notice you saying that your weapon is a sword. As there's only one job open to you at the moment (red mage) that can really claim sword as its "best" weapon, I'm curious about what job you've chosen. If you're a warrior, I know the intuitive thing to do (based on all high fantasy you've come in contact with before) would be to stick to swords, but the truth is, as a warrior, you're going to want to concentrate more on axes.