I'd suggest trying 2x2 binning to overcome the bckground noise and increase the signal to noise ratio. Its one way to increase SNR whilst you work on the flex so you can get longer exposures. 3nm was always going to need 15-30 min exposures to build enough signal.
I find 2x2 works well with my CDK17. You've got plenty of res there and you don't drop that much resolution anyway.
Greg I have processed the data with tone mapping which can accentuate the dim stuff all the way down to the noise without blowing out the bright stuff.
This is a stretched version without tone mapping 6MB