Mandarin Chinese (#13)

I learned a new way to ask questions in Chinese, as opposed to just adding the question word ( 吗 : ma) at the end of a declarative sentence. None of the content here is new for me, but what is new is the manner in which I'm asking the questions.

"Do you want to eat dinner with me now?"
"No, I do not want to eat dinner with you now, but I would like to eat dinner with you later."

"Do you have 15 元?"
"I don't have 15 元, but I have $15 USD."

[I've been told that the form I've used to say "American dollars" is incorrect, and that most Chinese people simply say "dol," appropriated from dollar, as slang for dollars.]