IIM Lucknow has been mentoring IIM Jammu since its inception. It has the same faculty from IIM Lucknow except for one or two subjects. The course curriculum is exactly the same as that of IIM Lucknow. The mentorship of IIM Lucknow is limited to the academics of IIM Jammu and it does not influence the placements.
The total course fee of MBA at IIM Jammu is INR 13,80,000. In 2019 the CAT cutoff of MBA for the general category and OBC category students was 95 and 78 respectively. The faculty at this university is quite good as most of the faculty members are from IIM Lucknow.
In terms of placements, IIM Jammu is still improving. According to the placement statistics of 2019, students were offered an 11.2 LPA average package and the highest package was around 24.5 LPA. Over the year IIM Jammu had more than a 10% increase in the average salary. The total number of recruiting companies that visited the placement drive in 2019 was 84.
IIM Jammu has also signed the MoU with ICAI (The Institute of Chartered Accountants of India) with a mutual aim of partnering together to offer executive training programs solely for the Chartered Accountants.
For a new institute like IIM Jammu, it would take time to get the cycle of big companies to come and hire from these colleges. As for whether or not you should join the institute the decision should be yours.