I Have UK LLB with 2:2 and Bar training course with 4 distinctions. I have got 4 distinctions in Bar training course. Moreover, I have 3 years work experience in one of the best Pakistani law firms. Can I get admission in JD or LLM in top 15 Unis in USA?

Your GPA seems a little bit low but considering your work experience I'd say you have pretty good chance to get into LLM in top15 Unis. You may need to take a LSAT if you want to apply for JDs so for JD I cannot say for sure yet.