I work for a service company and am asked to travel out of town but in state for 1 week at a time. I am being given 15$ per night I am out of town for meals. Is this a sufficient amount? Are they required to give me per diem at all?

No you mean 'preforma' and if you are out of town over night, $15 is not enough, only for meals. You need per diem, which will give you enough money to stay overnight in a motel.

I get 15$ each night I am out of town. They supply me with a place to stay. Is there some kind of place to find out if I am legally entitled to more that 15$

Do you have an employment contract?

Per diems are generally a negotiated perk of a job, not a legal requirement.

Let me see, 15 dollars, they are not required to buy your lunch normally since you would be doing that even at home.
But it is not much, but I could eat on that most places I would travel.

No contract. My employer sends us 5 hrs away. Just curious if they are required to pay us per diem

I would contact your local Dept of Labor, but I don't believe there is a requirement to pay per diems.