Yes, for this setup higher Irradiance subdivisions settings are recommended if you need more sharp and detailed shadows.
Also you may have noticed that the V-Ray Dome light has and advanced option (MIS) > this option allows to disable Multiple Importance Sampling for the light. When MIS is enabled (the default), the light’s contribution is split between direct illumination on the one hand, and GI (for diffuse materials) or reflections (for glossy surfaces).
It is ON by default and the noise level is being reduced a lot when using GI (Irradiance map mode for an example).