Paul doesn't mention Mosaic Law here, and it doesn't make sense here anyway.
If Jesus took away the Mosaic Law in v. 15, that occurred through Jesus' Crucifixion -- long before the conversion of Gentiles described in Eph 2:1-2.
Why would Eph 2:6-10 be talking about Mosaic Law anyway? Paul's talking about Gentiles, not Jews.
You pointed it out yourself, it's in verse 15. They are not saved by works because Christ abolished the Law. If you look into the background of Paul's ministry You'll find that one of the biggest problems he faced was that of the Judaizers. These were Jews who were telling Paul's converts that in addition to faith in Christ it was also necessary for them to keep the Law of Moses and be circumcised. This can be seen in Acts 15 and Galatians.
KJV
Acts 15:1 And
certain men which came down from Judaea taught the brethren,
and said,
Except ye be circumcised after the manner of Moses, ye cannot be saved.
2 When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas, and certain other of them, should go up to Jerusalem unto the apostles and elders about this question.
3 And being brought on their way by the church, they passed through Phenice and Samaria, declaring the conversion of the Gentiles: and they caused great joy unto all the brethren.
4 And when they were come to Jerusalem, they were received of the church, and
of the apostles and elders, and they declared all things that God had done with them.
5 But there rose up certain of
the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.
6 And the apostles and elders came together for to consider of this matter. (Act 15:1-6 KJV)
O foolish Galatians,
who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you?
2 This only would I learn of you,
Received ye the Spirit by the works of the law, or by the hearing of faith?
3 Are ye so foolish? having begun in the Spirit,
are ye now made perfect by the flesh?
4 Have ye suffered so many things in vain? if
it be yet in vain.
5 He therefore that ministereth to you the Spirit, and worketh miracles among you,
doeth he it by the works of the law, or by the hearing of faith? (Gal 3:1-5 KJV)
As we study Paul's writings we can see the evidences of this in them. There were those who taught his converts that faith in Christ was not enough, that they also needed to keep the Mosaic Law. That what chapter 15 of Acts and the Jerusalem council is about. In Ephesians 2 Paul tells his Gentile readers that they are "not" save by works so that no man can boast. He tells them no man can boast, what does he mean by this? Most Christians think he's talking about self effort, but he's not. He's talking about believers not being able to boast in their keeping of the Law. The Jews boasted that they were superior to the Gentiles because they kept the Law. Paul addresses this issue in Romans.
17 Behold, thou art called a Jew, and
restest in the law, and
makest thy boast of God,
18 And knowest
his will, and approvest the things that are more excellent,
being instructed out of the law;
19 And art confident that thou thyself art a guide of the blind, a light of them which are in darkness,
20 An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law.
21 Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal?
22 Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege?
23 Thou that makest thy boast of the law, through breaking the law dishonourest thou God? (Rom 2:17-23 KJV)
As you read the rest of Ephesians 2 it becomes clear that he is talking about the separation between Jew and Gentile being done away with and the two being made one. He says Christ has broken down the middle wall of partition. He is speaking metaphorically of the wall in the temple that separated the Jews and the Gentiles.