Over the past few decades, New Perspective on Paul (NPP) theology has spread everywhere and Eastern Orthodoxy (EO) has also been gaining popularity in the West. In my experience, it seems to me that NPP and EO people don't have a reasonable response to the doctrine of imputation taught in Romans 4. However, in debate situations, when presented with Romans 4:3, I have noticed that some of them evade it by appealing to Hebrews 11:8-9. In other words, they point out that Abraham had faith and was walking in obedience many years before Genesis 15:6. They think this observation undermines the plain reading of imputation in Romans 4 and requires a new reading of it, with redefined terminology, through the lens of covenant relationship (NPP) or transformation of life (EO). However, I don't think the plain reading of Romans 4 can be undermined so easily, because from my perspective, I feel like the Apostle Paul already anticipated this type of objection in Romans 4:2. What good works of Abraham was he referring to in Romans 4:2? It must have been those in Hebrews 11:8-9, etc. In addition, I think we have another example of this in the New Testament in the Apostle Peter's dealings with Cornelius. Peter testified of Cornelius by saying, "But in every nation he that feareth him, and worketh righteousness, is accepted with him" (Acts 10:35). Cornelius was accepted with God. God was pleased with his prayers and alms. However, as good as those things were, and regardless of whatever temporal blessings they may have procured from God, Cornelius still needed to hear the gospel and believe it to receive remission of sins (10:43) and be saved (11:14). I believe it was the same with Abraham. He believed God and was obedient before Genesis 15:6, but it wasn't until he believed the promise of God concerning his seed (i.e., Christ) that he was justified. I don't view Hebrews 11 as dealing with justification from the viewpoint of receiving eschatological life. It is more like a pep talk for struggling and suffering Christians to endure in their experiential sanctification so that they can receive rewards and inheritance (10:35, 11:6-9, 11:26) in line with the eschatological life they already possessed.
Furthermore, I think Genesis 15:6 does provide some leeway with regard to the timing of Abraham's justification. That moment most likely happened in Genesis 15:6, granted that it follows chronologically from Genesis 15:1-5. However, it is also possible that Moses was describing a moment of belief that happened many years previously in Abraham's life, such as Genesis 12:1-3, and was simply using the events of Genesis 15:1-5 as a springboard to introduce Abraham's experience of justification. Either way, Hebrews 11:8-9 does not contradict the doctrine of imputation in any way.