Late 2013 Macbook Pro Versus a Later Build
Without knowing which i7, how much RAM, and what type of internal storage your 2013 system and the 2015 system you're looking at has, I can't really compare the performance of the machines. If you replace your old machine with a 2015 i7 and with at least the same amount of RAM and the same type of storage, the new one will be noticeably faster, particularly in GPU-intensive applications like Photoshop, Final Cut Pro, AutoCAD, video games, etc.

The new MacBook also has a Force Touch trackpad, which definitely feels different than the old style trackpad.

You'll also get improved battery life (from an improved battery, improved efficiency, and the fact that batteries lose capacity over time, so any new battery of equal or greater capacity will last longer than any old one.)