My name is ***** ***** I will be assisting you with this question.
You're right. $15,000 is way, way, way out of the ballpark and incontrovertible proof that you've got yourself a romance scammer.
Whenever an online romance tells you that she has to show money to qualify for a visa, it's all you need to know to be sure that you're about to be swindled.
I know you'd like to believe your so-called "ladyfriend", because you probably think she's in love with you and vice-versa. But if you have any doubt about what I'm saying, you will find that Ghana's own Immigration
Service will tell you the same thing.
I am linking you to their site so that you can see this for yourself. You will find the warning on their the site's FAQ page, which you can locate from the column on the left:
Not only does Ghana not require money to leave, but the US absolutely doesn't require any foreigner to show money in order to enter the US. The US State Department warns of getting involved with a Ghanaian who is professing love to you online. As part of that, they warn about the BTA/Declaration fee as well, and say what I have already told you.
Our government's warning is right on the US Embassy in Ghana's website and reads:
"Beware of anyone who requests funds for a BTA, or Basic Travel Allowance, as a requirement to depart another country for the United States. There is no such thing as a BTA. In other cases, your Internet friend will claim to need a travel allowance, or travel money, to be able to travel to the United States. Again, there is no such requirement under U.S. law"
She has asked you for the one thing which even the Ghanaian government and the US Department of State say is an outright scam.
All a Ghanaian needs to visit you in the US is her passport (costs the equivalent of $35 USD) a tourist visa, (costs $140 and must only be obtained from the US Embassy in Ghana) and her plane tickets. Period.
You need to cease all contact with her and report her to your police if you sent her money and to the FBI at IC3.gov whether you sent her money or not.