Yield of alkyl chloride in the Hunsdiecker reaction
The Hunsdiecker reaction is a halogenation-decarboxylation reaction of silver salts of carboxylic acids.

To understand what causes the yield to change, first we have to consider the mechanism of the reaction.

As seen from the mechanism the homolytic cleavage of the $\ce{O-X}$ bond is the slowest step in the reaction and thus is the rate determining step. So as you predicted it all comes upon the stability of halogen radical. It's commonly known that the bromine radical is fairly stable than the chlorine radical and thus the Hunsdiecker reaction gives better yield with bromine rather than with chlorine.