I also think the problem must be the software, I have worked skins of that size on an i3 laptop with 6 gb of ram and the hdd about to collapse. My recommendation is that you can get an old Photoshop, maybe 7 to cs6 to meet the requirements of an modest pc, PS behaves quite well with documents of that size, you can configure virtual memory taking the free space of your HDD, another recommendation is not to go crazy creating layers and layers, you can make test layers that do not compromise the editing of other elements but once achieved the goal, you group them with related elements to go down the memory usage ...
... and something that I commented several years ago, a 4k texture does not have to weigh 20 mb ... nor 10 ... nor 6 there is an output in ps that is called “save for web” you give 90% or 80% quality (imperceptible detail loss) and you can leave textures in 2 or 3 mb what users with more modest pc hardware will be grateful.