I don't know. My well-off Jewish relatives in Russia don't report discrimination, but that I believe is a factor of their position or demeanor and not absence of antisemitism.
Since you asked "how big", I would say greater than zero but less than discrimination against certain other groups. These other groups include Chechens, other people from the Caucuses, people from the *stans, and gays. People in these groups are both more numerous and face worse discrimination. Non-Moscow residents are of course officially discriminated against in Moscow (Moscow residency is essentially a second internal citizenship that has been struck down by the courts but still exists in practice). Additionally 50% of the population are subjected to sexism to a significant degree.
Since you asked "how big", I would say greater than zero but less than discrimination against certain other groups. These other groups include Chechens, other people from the Caucuses, people from the *stans, and gays. People in these groups are both more numerous and face worse discrimination. Non-Moscow residents are of course officially discriminated against in Moscow (Moscow residency is essentially a second internal citizenship that has been struck down by the courts but still exists in practice). Additionally 50% of the population are subjected to sexism to a significant degree.