You can add more RAM, 4GB doesn’t even meet the min requirements of Lightroom CC IIRC, and they recommend 16GB.
I have a 16GB MBP and even that struggles (in that it’s slow) at times with LR, mainly as there’s never actually 16GB RAM free. I’m actually wanting to upgrade my MBP and would stick 64GB in, but the current prices are ridiculous.
I have the A7RIV and one way to reduce file sizes is to convert to Adobe DNG, this takes them from circa 120mb to circa 65mb by adding lossless compression. To date I have witnessed no ill effects. That being said file size is one thing, but it still has to render/deal with all those pixels which can slow it down.
Last thing to mention is that there have been reports that the A7RIV doesn’t always play nice with the 200-600mm.