Really 16000 px wide ?
It's for a 360 sky texture, for 3d rendering. It's necessary given how much it has to be stretched.
I think you can try in Foundry Nuke.
Why would that even be necessary? You could just layer the textures in your 3D program and set the value ranges to be used by the renderer there. Otherwise this would require some heavy surgery with separating the different exposures first, transposing the luminance info to your high-res image and merging everything back to a new HDR document. Doesn't really make much sense to me to jump such hoops, especially if you only have Adobe tools at hand where this is like pulling teeth.