You would probably need bigger dish as 15% is not so little.
For Astra 2D I would also recommend an offset dish, because of more shallow beamwidth + offset dish have a little more gain than primefocus of same size.
I would recommend a Channel Master 2.4 which is actually 2.66 x 2.5 m in size, but be warned that you're walking on very thin ice. Quad QDF-031 is the way to go, as it gives more signal than its Twin brother.