I know it is a tough decision because I have seen my sister in a similar dilemma last year. What she did was focus on the below 3 aspects and made a decision.
Work Experience: It’s not understandable that with a work experience of 3+ years why you are only targeting IIM Lucknow and not other top IIMs like A B or C. Also if you don't want IMTG, you should wait and give GMAT and try for ISB.
Educational Background: Your chances of getting into IIM Lucknow next year depend largely on your past academic records which cannot be changed. So you need to ensure they are enough to make you eligible for the cutoff and worth the wait.
Lastly, you should be confident of the risk you are willing to take. Choosing IMTG vs IIML is a no-brainer. So check whether you are choosing IMTG just because you are not confident of being able to get into IIM Lucknow next year or not.