With an i7 processor, you shouldn’t be having problems with choppy audio. One suggestion - check you haven’t got 2 instances of Shotcut running. SC goes very slowly if you have. It’s easily done if you double-clicked when you started SC.
Never been a fan of mp3 format.
Have had too many problems with strange bit rates, latency and hate that small bit of silence at the start and end of many mp3 files.
Since you have Audacity, why not convert to PCM(WAV) or something like FLAC if WAV creates files which are too big.