version 15 works correctly up to the 376 epoch. The new version is not needed yet
when using Windows the first GPU takes something like 140-150 MB more video memory on top of the other ones that are just mining, so with that the actually used video memory gets closer to the 4GB limit and instead of 20-30 MH/s you might be getting just 1-2 MH/s for the first GPU and soon it might even stop working.
First GPU always use more video memory for system stuff.
So the main problem does not depend on CM version but on size of the DAG file required to mine etherium and loaded into the GPU memory. The DAG size increases by 8MB in a few days when the epoch changes. Therefore it's inevitable that soon 4GB GPUs will no longer be able to mine ETH, as happened in the past years for the 2GB / 3GB GPUs.
In short term some workarounds could be:
1) Use a different PCI slot (different from first: PCIx16_1) for 4GB GPUs or enable integrated GPU.
2) Switch to linux which uses less memory for first GPU.
Personally, although I am still able to mine ETH with CM 15 / WIN10 even with a 4GB GPU in first PCI slot, sometimes when the epoch changes the hashrate decreases, I have to manually restart CM or Windows. In my case, other miners no longer work for 4GB GPU: they already start working with a low hashrate.
IMHO there is no point in that. Any GPU with attached monitor will be the first GPU and will display dektop , eating memory from GPU, so it will have less RAM to hold DAG file and we will face this issue.
I think of 3 ways : 1. GPU0 with 6-8 Gb RAM. 2. Inegreted GOU 3. Linux distro as it consumes less RAM.