8GB RAM vs 16GB RAM?

Many today recommend 8GB for the minimum RAM to run the modern macOS. Mojave will be no different.

The price of RAM is a bout a third of what was when your 2012 was new.

RAM Memory Upgrades for MacBook Pro 2012 - 2015

Running your machine on 16GB of RAM may help you with an informed decision, when you have to replace your Mac with a new machine. Then the question becomes 16GB or 32GB.

I would recommend no matter what you decide, when you swap out your SSD, I highly recommend a new SATA cable at the same time, to avoid any issues or disappointments.

Apple 821-1480 Hard Drive / SSD Cable For 13-inch... at MacSales.com

OWC/McacSales has excellent customer support— you can ask them about compatibility.

If you buy a kit: SSD/external enclosure/tools your rotational HD can become and external backup device.

How to create a boot clone

It is a "possibility" Mojave maybe the last software upgrade for the 2012.

MacBook Pro (15-inch Mid 2012), macOS (10.13.6), i7 480GB SSD 16GB RAM

8GB of RAM, especially with an SSD, should be plenty for most people. However those of us who tend to keep lots of tabs open in our browser and run multiple programs will notice some improvement with the additional RAM. That said, even though my desktop has 16GB and my MBP has 8GB I've seldom felt my MBP was at a disadvantage due to RAM. Then again, I don't use Chrome which I think is insanely RAM intensive.

Crucial Tech and OWC (macsales.com) are my 2 hands down choices for RAM. Quality product and superior support.

I have the same MBP with a 500GB SSD upgrade. It has 8GB RAM and Activity Monitor has never showed in starved for RAM. However, I would never let Chrome near my Macs due to its inexcusable penchant for soaking up every possible resource, and I don't do XCode. The most taxing thing my MBP sees is PhotoShop Elements.

With developer software on the plate and an new OSX release around the corner, I think I would lean to the 16GB upgrade if it is within your budget. And i whole-heartedly agree with my esteemed colleague dwb's vendor recommendations. I've bought all our Mac RAM for our Macs and those I maintain for friends from OWC for probably 15 years and have always received the proper product that worked perfectly. But online to get proper RAM.