Approximately 600 thousand of 15-year old students from 79 countries took part at PISA-2018 research and among them 7608 were from Russian Federation.
According to the recently issued report of Fededal Institute for Education Quality Assessment (FIOCO) overall average score has decreased compared to 2015 results.
Average score of Russian pupils on reading performance is 479 points whereas a previous number was 495. Mathematics and science literacy scores are no good with 488 points in 2018 and 494 in 2015, and 478 (487). Nevertheless, it should be noted that in 2015 only pupils from schools of Moscow took part in the study, whereas in 2018 the sample included students from Tatarstan. Despite overall decrease the results of Moscow pupils increased in 2018. That gives some food for thought on the gap of education quality between capital and regional schools, revealing that it is plenty of work to be done to close it.
You can find detailed information at PISA-2018 in Russia at FIOCO website.