I really think that 1.5 is impossible for a soft sail. simply impossible

this because the shape can never be consistent because of the nature of cloth
add to that they are encumbered with the mast and rigging which influences the flow

in the real world airfols on purpose built aircraft struggle to improve on CLMax 1.2 OOGE without flaps or slats
and that is there cleanest, therefore least drag situation

high tech laminar rooftop foils do improve on this, but they are required to be fractionally mm accurate and very clean to keep their boundary layer closely attached to the surface. The tolerances are so fine that even water or grit on the foil will break the flow and subsequently destroy performance. Think about how that might compare with a sail where you have far less control over shape

and even yet, it has been found that laminar rooftops are impractical for general aviation use were more usually very basic and quite often old airfoils dominate

there are so many things I feel I do not know about the all round operational characteristics of wings on boats that makes me hesitant to to do little else but ponder the issue further, but sails with a CL of 1.5 I simply wont accept