Ed Sirett wrote:

Someone will correct me if I'm wrong but I'm fairly sure that you use the
red crimps on 1 and 1.5mm² and the blue on 2.5mm².

Either red or blue should be OK on 1.5.

Red: 0.5 - 1.5 mm^2
Blue: 1.5 - 2.5 mm^2
Yellow: 4.0 - 6.0 mm^2

--
Andy