“We were able to raise just under fifteen thousand dollars.”

You were in charge of planning an event to raise money for a charity. Now the event is over, and you're talking to a friend about how it went. You're telling him about the amount of money you made:

We were able to raise just under fifteen thousand dollars.

(someone) was able to (do something)

The phrase "able to" is similar to "can", but there are a few differences in their use.

When you're talking about something that happened just once or just a few times in the past, don't use "could"; use "was able to":

I had a good time, and I was able to meet a few famous jazz musicians.

raise (an amount of money)

To "raise money" means to get money from investors or donors. Investors are people who lend you money to get a piece of your business, so that they can earn more money later. Donors are people who give their money for a charity, a school, etc.

You can use the phrase "raise money":

We're raising money for cancer research.

Or you can state the amount of money:

We're hoping to raise $100,000 for cancer research.

just under (an amount of money)

"Just under $15,000" might mean $14,600 or $14,900. It's a number that's under $15,000, but very close to it. One reason for using this phrase is to make the number sound bigger than it actually is. "Just under a million" sounds larger than "nine hundred, seventy five thousand" (975,000).