Hey there, samlky!
I don't think it's actually going to work. Even if it's still a MacBook, the models are different. It's highly unlikely to boot but if it does, you will surely have problems with the hardware components and drivers. Since both computers are using different hardware, i.e. processor, video graphics, RAM, etc., there is a very slim chance the swapping of the drive would work.
Not to mention the fact that you are swapping from an almost 5-year-old machine to a new one, a lot has changed in the past 5 year in the computer technologies.
Better backup your SSD and HDD to an external drive and once you have the new MacBook simply transfer all the data you need but a fresh install of the OS X is essential.
Even if you want to use your current SSD on your new MacBook, you'd need to reformat it and perform a clean install.
Hope I helped! Good luck!