All things being equal, does 4th gen quad core i7 (2.5GHz) need more RAM than 5th gen dual core i5 (2.7GHz) for same tasks?

• Bought mid/late 2014 15" MBPr with the i7 2.5GHz and 16GB RAM. I'm within 2 week exchange period at Best Buy, and thinking of switching to 2015 13" MBPr with i5 2.7GHz and 8GB RAM for battery life and weight, and they don't offer the upgraded 16GB RAM option for any 13" models.
  • Needs to be Best Buy because of gift cards
  • Use docked at office 75% of time vs 25% out of office, so portability and battery life are nice to have but not as important as if I had 8 hour flights on weekly basis
  • See appeal of having 5th gen i5 in 13" vs my 4th gen i7 that will be updated this summer
• Not a gamer and don't use Final Cut or other video editing, but I tend to leave several applications open and usually have between 1-3 GB free RAM of the 16GB total at any time according to my Memory Cleaner readings
• Therefore, worried that 8GB is a non-starter as simple math says that I would have shortfall of 5-7GB RAM based on above readings, but wondering if dual core i5 will use RAM more efficiently than quad core i7

Any help greatly appreciated!