No hard data, but there is circumstantial evidence.
1) As
@Scchwerter_ stated there is official confirmation that J-16 uses radar absorbing paint in some areas. This is in fact confirmed by Golden Helmet pilot Jiang Jiaji.
2) Taiwanese air defense makes a distinction between J-16/Su-30/J-11 even when they don't scramble fighter aircraft for intercept, implying that the radar signature is different between the three types.
3) There is a leaked document instruction for ground radar operators that participated during the 2017 parade in Zhurihe. According to the said document, J-20 (with lunesburg lens) and J-10C can be difficult to track via radar since the signal return is weak and intermittent, in contrast to flanker types like J-16.
Based on the aforementioned points, we can conclude that
1) J-16 has RCSs reduction measures done.
2) It probably has smaller profile than Su-30/J-11B, but doesn't come close to J-10C or J-20 with luneburg lens.