I just see, that the OpenEXR again lost its connections. But normally I have a render layer chosen and connected all the passes with red marked nodes …
If your EXR files are made to preview quality then you definitely have to do at least some re-rendering. Or do you already have better quality sequences rendered out? If so, then just change the nodes to load them.
I’d stick with the image (EXR) sequences: render each of the render layers with better quality and then use ALT+R to reload them into Node Editor. This way you don’t have to reconnect the nodes again. (Although, there is a shortcut for that. See https://www.youtube.com/watch?v=-ZukeYlyXv0 and try the same but drag the line over all of the noodles coming from a single output of one node.) You can use the Render Layer -nodes instead of the Image Sequence -nodes if you want to but for the sake of production pipeline -thinking it might be better if you re-rendered the Render layers separately and did the composition with the EXR-files.
The composition render should indeed be faster with EXR-files. I’m actually not quite sure if you need the high sample count any more if you do the composition-render with the EXR-files but likewise I don’t know if lowering it will make the render any faster either. You won’t be rendering the 3D scene but the 2D image sequences. In fact you could change to Blender Render if you wanted to but that probably won’t do any difference.
Hey,
sorry was offline for a few days. I wanted to say many thanks for your help. It worked out 
Thanks for your patience and your good explanations …
thx.
t.