I had my CVH at 15:1. The CVH never handled lean situation too well. Didn't run well at all above 16.5:1. Compared to modern 16V engines for example that seem well fine upto 20:1 without any hesitation.

I always liked to keep my CVH lean at cruise because it seemed to have a great effect on keeping the plugs, valves and chambers completely clean. Cruising with a rich mixture leads to carbon buildup quite easily which promotes other issues in the long run.