Query about total years of backlog permitted in BTech

Generally, you will be given 3 years additional time for completing the B.Tech course study period. You will be completing your 4 years of study by 2020. Whatever backlogs you have should be completed by 2023 March. If you are not completing by that time you will be getting a " Not Fit for Technical Education (NFTE) certificate" from the university where you studied your B.Tech. Once you were given this certificate you can not get admission in any professional course. It will be a black mark for you. So you should concentrate on your studies and complete the subject within that period. I suggest focusing more on education. Hard work will always pay good dividends. Don't get diverted from the main issue that is education. Study well. Put extra efforts. Be in touch with your teachers and other seniors and clear your doubts. Take old papers and answer them. Read books and understand the subject. Then you can complete your course.

As you have mentioned that you joined I have joined BTech in 2015, You total years will be in continuity i.e a total of 8 years from the year you joined B.Tech (2015 - 2023). The gap or detained or drop in the middle is due to your backlog that you were not able to clear within the prescribed time allotted by the university.

You need to understand your university rules which allow a certain amount of backlog that you can carry forward to the next semester/year but need to clear within the next year or else you will not be promoted to next year. Once you clear that subjects or the total no. of subjects that are allowed by the university to carry forward, you can continue in the next semester/year.

The Engineering college/university allows 8 ATKT's in total (5 External and 3 Internal i.e. viva, practicals, Unit Test) as per new rules and also you will have to clear all your 1st year ATKT's before the completion of 2nd year i.e while giving your 4th-semester exam or else you will get a drop. Also, note that even though you clear your previous year backlog but have exceeded the total number of ATKT's that you are bound(8 nos) to, you may get a year gap and the rules follow for all semester/years. So as per university rules, one gets a chance to clear his/her backlogs or ATKTs (1st sem backlog to be cleared in the next 3 chances 2nd, 3rd and 4th semesters & 2nd sem backlog to be cleared in your 3rd and 4th semesters).

Different universities have different time exemption period in this regard and mostly it varies from 2 years to 4 years. In your case you joined the course in 2015 so you have to find from university whether you would be allowed to cover the arrears up to 2021 or 2023. Further, please make a note that time to time some universities announce special packages for the old students who are desirous of clearing their backlogs at a later date so that aspect also to be kept in mind.
As regards to your backlog or arrears it would be better to take them up sequentially as many as possible at a time so that your future load is decreased considerably. More you clear now will be better for your later semesters. You will have to change your entire study strategy as casual studies or limited studies and guesswork about exam papers will not be helpful to you at all.
I would advise you to take up at least 2 papers from your backlog and try to appear in them along with the papers prescribed in the present semester. Take help from the students who have already passed in those backlogs. You can even join some tutorial classes and take help from the lecturers. Please note that if the university gives an opportunity to cover the backlogs in some extended period, it does not mean that one becomes slack in ones studies. This is the prime time of your life and wasting 2 to 4 years is a big risk as job opportunities would further shrink in the market and you will remain a laggard in career making. Please wake up and assimilate your mental faculties to work hard and clear the backlogs and come to the normal situation. All the best.

Since you have indicated that you joined the B.Tech course in 2015. In the normal situation, the tenure of completion of the course is four year but here is a catch that you were not promoted to the third year classes in the year 2017. Taking this factor into account, you should have completed the course in 2020 supposing that no backlog took place in your academic session.
According to prevalent rule of clearing backlogs applicable to all universities conducting BE/ B.Tech is three years and hence you need to clear all your pending backlogs by 2023.
Failure to do so will lead to cancellation of your degree with a certificate indicating Not Fit For Technical Education. In that way, situation in your case will be very critical with the loss of so many precious years.
The situation demands your dedicated efforts. Remain in touch with the professors for the subjects which need to be cleared. Follow their advice and at least go through the question papers of last five years. In most of the times, questions are repetitive in nature and such a meticulous planning will help you in clearing the pending papers within the alloted time.