Continuing with Rom 2:
16In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
17Behold, thou art called a Jew, and restest in the law, and makest thy boast of God,
18And knowest his will, and approvest the things that are more excellent, being instructed out of the law;
Here The law is noted as being more excellent and the will of God. It is also noted that the secret things of the heart would be judge by it, no wonder then that Jesus could have said that if you look at a women and lust after here you already commit adultery.
19And art confident that thou thyself art a guide of the blind, a light of them which are in darkness,
20An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law.
The law here is termed the truth and from the context it is seen that those who did not know it were foolish, in darkness, blind and immature.
21Thou therefore which teachest another, teachest thou not thyself? thou that preachest a man should not steal, dost thou steal?
22Thou that sayest a man should not commit adultery, dost thou commit adultery? thou that abhorrest idols, dost thou commit sacrilege?
23Thou that makest thy boast of the law, through breaking the law dishonourest thou God?
The context demonstrates clearly the 10 commandments is what is referred to.