The struggle is usually memory. Every render pass in a multipass render will require more memory, and this grows more significant the larger the resolution. So, you can remove render passes, with particular attention to LightSelect passes, the less of those you can use and still have enough control in LightMix, the better. Denoising also needs more memory, again for every pass it is enabled on (such as LightSelect passes), so you could use "Save Data for Later" and Denoise in the CIE, this may help. Or you could turn off Denoising altogether and simply render for more passes, if memory remains a struggle.
You can then also render in strips, and recombine later in post to give the full final image.