First, congrats on hitting level 15!

Couple things on gear:

1) Check Yellow Gremlin. It has lists of available gear, and you can sort it by level. It also has average/mean prices, and it shows whether it's being sold by an NPC, and where the NPC is located. So you'll know which gear to keep an eye out for.

2) There's not a huge amount of low level gear available in the market wards. So the folks that are selling low level gear sometimes charge an arm and a leg for it. (Partially because they can, and partially because it's the only way they think they can make a reasonable profit selling it.)

3) Having maxed out gear is not too important at low levels. You can get by in starter gear until probably around level 20. The exception -- as Astray said -- is your weapon. You'll want to use the appropriate level weapon.

4) Some quests and leves offer gear as rewards. Keep an eye out for those. Free gear!

5) Join a linkshell. Probably the easiest way to get new gear is to get hand-me-downs from other linkshell members. Or, if there are no hand-me-downs, you can probably get crafters to create stuff on request, if you can provide the materials. Plus, the community in this game is pretty great. They're helpful and mature and knowledgeable. You'll have more fun playing with others, and they'll make the game much easier on you. I cannot recommend joining a linkshell strongly enough.

As for money, it's pretty tough going at first. But eventually, you're going to be surprised how easy it is to make money in this game. Just NPCing mob drops, and getting leve rewards, you're eventually going to have more money than you know what to do with. By the time you get to level 33 -- when you start doing r40 leves -- you're going to be able to get 30K+ from one leve. You'll usually pull in around 100K or more from a complete set of leves.

Like Astray said, sheepskin are in pretty high demand right now, so you can make some good money off those. (They're used for both low and high level grinding in Leatherworker, and they can also be used to grind Alchemy.) You can also sell crystals/shards that drop from mobs. Wind shards and wind crystals tend to sell the best.

Another option is to take up fishing. Low level fish aren't particularly high demand, but even mid-level fish sell really well.

As in every other MMO, the best way to make money is to level up a craft and start selling stuff on the Market Wards. But that will take time, and often takes a pretty significant investment of money in itself.

But overall, I'd just suggest patience. Seriously, you're going to end up having more money than you can reasonably spend. The leve and quest rewards get better the higher up you level. And the faction leve rewards can be pretty spectacular. (More than once, I've gotten over 50K gil from completing one faction leve.)

Welcome to the game. And good luck!