Just a guess from 26 years of windsurfing - .65 kg of weight difference between the WC and W boards will not make a noticeable difference in the planing threshold for the 144, especially for someone at your weight. I used the word "noticeable" since there probably is a very, very, very small difference, just not one that could be measured.
I still think the 150 is your best bet for your under 15 knots wind range. As for sail size, I can only speak to my experience with my largest sails - Maui Sails TR 9.2 and 11.0. There is a very noticeable difference in power and early planing between the two, especially between 8 -12 knots on my formula board. I weigh 78kg (170lbs).
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.