Question: Should someone that has never had a credit card before check his/her credit score before applying?

Answer: 
Please, please don't believe all the financial sales pitches you will hear in your life. Consistent?? give me a break. The returns promised include the effects of leverage. That same leverage can also generate 100% losses.
To make a return of 15% on $100k the currency you are trading would have to move by 15%. This does not happen to often. In FX trading you are mostly trying to capture and profit from small moves in a currency pair.

Based on this, in my opinion, the 15% return would be based on your own capital, ie. the $1000. This would be how I would work out my return when dealing with margin.