Yes, your RIOS 12th certificate from the 2015 batch is generally valid for jobs in private limited companies, especially since you also hold a degree from North East Christian University.

RIOS is recognized as a state open school board, and such certificates are usually accepted by private companies for job applications. The fact that you were able to pursue and complete a university degree also supports the validity of your 12th certificate. Most private companies focus more on your overall qualifications, skills, and degree rather than the specific board you passed 12th from, especially if it is recognized.

While a few top-tier or highly formal companies may prefer candidates from CBSE or state boards, most LTD companies will not have an issue with your educational background as long as your documents are in order and verifiable. You should be able to apply for jobs.