Good morning! Maybe I'm looking for a pep talk, but honestly, I just want a no "bullcrap" outside perspective if I should jump ship or stick it out:
I just completed initial sim training at my first ever airline gig. I was a prior CFI with no prior turbine experience. During training, I passed my MV and LOE first attempt, but I struggled tremendously and had to do several repeat lessons. I feel like my performance was marginal throughout training, even during the checkride, and now I'm have some serious jitters for IOE which will be coming up in a few days. I know people say IOE is fun, but for me, I feel like I'm still not safe.
Going through this training for the past 2 months has really taken a toll on my passion and interest for flying. I have contemplated resigning several times during training to do something else not in aviation field and have asked myself if I'll even enjoy the professional airline life. I want to be loyal to my airline because they invested so much in me, but as the title says, I'm having cold feet.
Your post is one of the best and most honest I've seen in a long time. Questioning oneself is a key sign of intelligence and responsibility. So, don't quit because of that. At least not because of that alone.
Now let's address the elephant in the room. You have just entered a venue that is rife with ego and "swagger". Today, we all like to say those kinds of things no longer exist in our "industry". Yet, definitively, they still do. Much for the worse, today we are secondarily infected with "sensitivity training" and other empty appeals to be "nice" in the face of incompetence. We are infected with warehouse-size volumes of undeserved senses of entitlement. We are infected with many, many, many people -including many practitioners- who really believe that what we do is "just another job".
The perfect pilot is the perfect balance of confidence and humility. Despite all the acting and presenting that goes on around aviation, the fact is that for a reasonable, intelligent person, both the confidence and the humility come from the same place: the house formed from the three axes of: competence, experience, and knowledge.
Questioning your readiness is a great sign. There is very little margin for error in flying airplanes. So questioning your readiness is important. More important is
knowing that you need to question your readiness. Without knowing the details of your situation, in general, the fact that you are asking says almost all that needs to be said.
It sounds like right now, you have little experience upon which to assess your judgment of your readiness. So, your doubt is reasonable. Yet, it also sounds like you are aware of what you don't know. Knowing what you don't know is a key attribute to excellence in all endeavors, most importantly ones in which incompetence can kill you or others real quick like.
The only obvious exception that jumps to mind is skydiving, in which the motto has always been: "If at first you don't succeed, Skydiving is NOT for you."
Carry on carrying on! Ask lots of questions. Fill in the gaps until you feel like you're solid. One day, you'll have the perspective to look back and say, "Boy, was I ever stupid to question myself!" And, at the same time, realize that... NO, you weren't! Questioning oneself is what a good pilot should be doing every day!