Sweet Autumn is a pruning group 3, which means that you cut it down to 6-12" from the ground every year. Mine grows from 6" to 15 or 20' every year with really good coverage. It's a very large clem, so I think it's exactly what you're looking for. One year I wanted to see what it would do if I didn't prune it at all, and it still was 15 - 20' tall. I had thought it might add an additional 15' to the 15' from the previous year, but it didn't. I cut mine down in the fall to let the lattice it grows on dry out and because the dead leaves look ugly, but if you didn't want to prune at all, I think you might be able to just leave it alone if you didn't mind how it looked in winter. The only reservation I have is how the spruce roots from the other trees might affect it and I have no advice for you about that, I'm afraid.

With a couple of caveats, I think the SAC could work for you also. First, you should be aware that this is considered an invasive species in some areas, mostly in the Midwest and east coast I believe. Second, it can grow quite a bit larger than 15-20'. In my garden it grew to 30'+ each season and could engulf all manner of plants anywhere close to its location. I would not consider that a real handicap for your situation, however conifers like the spruce often react poorly to being covered/shaded by other foliage. If you can keep most of the growth restricted to bare spots on the conifers, you should be OK.

FWIW, I would NOT consider leaving this vine unpruned - it would not be beneficial to the conifer at all. The weight and shading of the accumulated vine would rapidly become detrimental.

Thanks. So treat it as the group 3 it is, prune it to the ground and pull everything out of the tree every year. Thanks again.