I recently bought inspiron 15 7559 i7 and found that the keyboard is bilingual.
It's little bit hard for me to type as the enter key is really small.
Would it be possible to get another keyboard (with different layout) and replace it?
You can likely find a non-bilingual keyboard, but that won't change the enter key - unfortunately the keyboard is proprietary to the model and cannot be changed to a different model. If you're not happy with the system, you can return it and order a different model within the first 21 days after shipment from Dell (or according to your reseller's policy). Otherwise, the only real option is an external keyboard.