Is it better joining IIM Trichy (new IIM) rather than joining Infosys as a system engineer?

Preparing for the CAT again is a hefty task and requires a lot of motivation. So I will suggest that you forgo your offer to join only under the following circumstances

1. You have a good past academic record. IIMs lay great weight on past academics and it is something that cannot be changed even after getting 100 percentile in CAT.
2. If you are confident that you can prepare for your CAT alongside working at Infosys. That company is said to have an enormous workload so you need to be sure that you can prepare for CAT efficiently simultaneously.
3. If you are targeting older IIMs like A,B,C,K,L 

If your situation does not involve any of the three cases then going for IIM Trichy is a wise decision. It’s a second-generation IIM and older than the newly established IIMs. Moreover, you will still get the IIM tag, and chances are that by the time you pass out from the institute, it has gained more reputation.