SU 35 sensors are battle proven. That's right, if US starts serious upgrades on F 15s it can become a threat in the future. Aviation industry is not black an white story
For example
Su 35 chased away an F 22, US denied but it happened during a political stand off. It's true story, in Syria, Russian fighters did great, they could safeguard SAA FROM coalition bombardments. F 22 failed to impose a serious threat in the Syrian sky, in many cases SU 35 neutralized threats of coalition airforce under American lead.
Americans are aware of their technological failure, just note that most of Arab countries which were former buyer of American military hardwares, turned to Russian equipment. An other sign of American failure in military markets. E.g. UAE buying SU 35s