How to turn 4k still images into smaller resolution to edit in Premiere Pro?

Hi, I am editing a wedding video with Premiere Pro CC 2017 on an iMac (Retina 5K, 27-inch, Late 2015)  4 GHz Intel Core i7 16 GB 1867 MHz DDR3.

I am having an issue where after about 10 min of editing, Premiere starts gobbling up my RAM pushing it into the red on the Activity Monitor, sometimes pushing up to 30 GB (and I am not sure how this is possible since my iMac has a 16gb memory?)

With no other applications open, it gets to the point where the "Your application memory is low" error message comes up and then asks me to force quit other applications to free up space. My comp then freezes up and I have to force quit Premiere.

I've talked with Apple Care, they say it is an application issue.

I've talked with Adobe support, they suggested I create a new user account with Admin rights and see if it works on that account better. They then suggested it might be the individual project that is causing this issue. I opened up another project with much more footage, things ran smoothly.

SO I have narrowed it down the the possibility that the still images I am using in this video are too large in resolution. They are 4K images. "Oh duh, I'll make proxies and work with a lower res version" Except no, Adobe only lets you make proxies with video, not still images.

So my question is, does anyone have a recommendation on how to essentially make still image proxies that I can edit with and then exchange for the high res images once I am ready to export? Does anyone else run into this issue?

I've also read that there could be a memory leak, but with the issue not existing in the other project I am not sure that is the problem here. Any help would be tremendously appreciated, thank you!!