There is no certainty if a gap of 4 years between BTech and MTech will affect placements in any way because it all depends on what you did during the gap. If you were working, then your experience will have neither a positive effect nor a negative effect as the recruiters come with fixed roles and packages and it’s not MBA so the gap does not really matter for them.
Before joining MTech you can analyze what the current job will give you in 2 years in comparison to the MTech degree. Only then make a sound decision. All in all, you will require more than normal efforts to get into MTech.
Some points pertaining to MTech in general and its placements specifically are mentioned below:
To make the most out of your MTech degree, you have to invest maximum effort and then reap the benefits.