It was an adjustment. Going from doing whatever you want (flying upside down, 4k fpm descents, etc) to the strict 121 environment was a big change. I look back on my skydiving days as the most fun I've ever had. Flying Tprops is close, the crews are awesome, planes are trucks and it's challenging.

My transition was eased because I was flying a Duchess on the side, doing cross countries IFR all the time the year prior to getting hired 121. Initial sim training is almost all IFR with emergencies for a week straight... not a good time to reinforce weak instrument skills.

My personal recommendation is to not only get current, but proficient before starting. It will help you in the long run and make absorbing the million other things in 121 training easier.