Firstly DTU is concerned only with your JEE mains scorecard not with your state board exam results.

Now since you are from RBSE, so it would be an other state candidate and this would add difficulty for you in your selection.

So in 85.25%ile your rank would be around 1.2-1.3 lac.

Considering this rank, your state and category you would have almost nil chance of getting a seat at DTU.

So according to me, the best possible available options are

1. Prepare well for state exams like WBJEE, UPTU and GGSIPU. Trust me, some state colleges (which these exams offer) are far better than bottom 15 NITs

2.  Prepare well for BITSAT for a month. With rigrous study for a month you can expect to have a score 300+. From this you can easily expect a seat from BITS GOA which is better than any of NIT (leaving top 5)