Chiming in kinda late, but I was having this exact issue on my Windows machine that's definitely capable. i9 9900x 4.7 on 10 cores, 64gb 3200 cl14 ram, 2x 2080tis. I opened a support ticket with Insydium and they got back to me promptly. Turned out it was due to Acronis running some sort of "Real Time Protection" in the background. When I turned that off, I was getting silky smooth eXplosia sims.
It should definitely be running fine on your machine since I tested it on the old/slow 2013 Xeon MacPros at the studio and was getting smooth playback. Not sure what else you have possibly running in the background of your system, real-time backup of any sort maybe, might be worth a check. Acronis wasn't showing any cpu usage at all, but was somehow causing sims to chug like yours 1-5fps max, unable to cache. Open a ticket with them and they may be able to point you in the right direction as they did for me. Good luck!