I have completed class 12th in science in 2015. Can I pursue B.Tech?

Yes, surely you can pursue B.Tech if you had science in 12th.

Most colleges or rather every college allow a 1-year gap only after 12th and even in some of the competitive examination preference is also not given to dropouts but you can get admission in some colleges. If not, then go for other professional courses.

Yes, there are many colleges in which you will definitely get the admission but there is a certain number of colleges in which they set a lapse restriction. Kindly check that before you apply.

If you had maths then you can surely pursue B.Tech.