You wonder what the actual range of the picture is? Here is a way:
ContourPlot3D[5 x - 2 y + 7 z == 15,
{x, -7, 7}, {y, -7, 7}, {z, -7, 10},
Mesh -> None, ContourStyle -> Yellow,
AspectRatio -> 1]
AbsoluteOptions[%, PlotRange]
You don't like the range of the picture, and need to make your own? Here:
ContourPlot3D[5 x - 2 y + 7 z == 15,
{x, -7, 7}, {y, -7, 7}, {z, -7, 10},
Mesh -> None, ContourStyle -> Yellow,
AspectRatio -> 1,
PlotRange -> {{-10, 10}, {-10, 10}, {-10, 10}}]