Something to think about is the case capacity the 155 Scenar uses up because of the way it's made. Overall it's about the same size as a 175 SMK. I'd think the 45-46 grain range is good.

With a flat base 150 I use over 47 grains of Varget in Lapua brass, but that's a much shorter bullet. Based on my experience with 165s and WWs needing more Varget than Lapuas, I'd have to head toward 48 with the 150. But again, that's a much shorter bullet than a Scenar.