About to buy a new Macbook Pro and I need some quick advice!

Hi!

There's a MILLION people who have asked a similar question and for that I am so sorry haha. I have scored the internet but I haven't been able to find an answer for my specific question so here goes nothing. 

I am buying a new Macbook Pro in a few days. I love the Sims4, but I don't think I love it enough to get the 15" MBP with separate graphics card because that laptop is just way too big for what I need it for (school). This was already a really hard decision to come to but I'm pretty much set on the 13" MBP. There are options to upgrade certain aspects of it, and I have tried so hard to understand what all the specifications mean but I just don't have enough experience with this stuff.

On my currrent computer, the Sims4 takes up 21.33 GB of storage. I have 3 expansions and 2 game packs and would like to get a few more  eventually (but I'll never be getting all). My current computer is a 2012 Macbook Air (lol) with the following specs:

Processor Name: Intel Core i7

Processor Speed: 2 GHz

Number of Processors: 1

Total Number of Cores: 2

L2 Cache (per Core): 256 KB

L3 Cache: 4 MB

Memory: 8 GB

I play on mostly low settings (objects and lighting on medium, 3D scene resolution on high), the game lags but is still playable. I would ideally like to be able to play on medium/high settings on my new computer, without lag, but I understand that not getting the 15"MBP with the dedicated graphics card will limit how high I can set things. 

Can someone help me with finding out if any of the following upgrades would significantly improve my gameplay (higher settings/less lag)? If more than one would, how would you prioritize them?

Things about the new computer I CAN'T change:

• Macbook Pro 13"
• Intel Iris Plus Graphics 655

Here are the things that I CAN change:

2.3GHz quad-core Intel Core i5, Turbo Boost up to 3.8GHz, with 128MB of eDRAM

• Configurable to 2.7GHz quad-core Intel Core i7, Turbo Boost up to 4.5GHz, with 128MB of eDRAM

256GB SSD

• Configurable to 512GB, 1TB, or 2TB SSD

8GB of 2133MHz LPDDR3 onboard memory

• Configurable to 16GB of memory

Would upgrading any of these result in significant improvements in gameplay? Let's pretend money is not a concern (but keep in mind that the less upgrades, the better). Thank you SO much!