Audio delay on Mac Mini Pro 4

I am using a Mac Mini Pro 4, editing 4K footage. Using a San disk Portable SSD for virtually all the footage. I have a second close-up sound track to several interviews which was recorded on a Canon Camera using MTS format. I can edit more or less fine, however, when I try to play the footage in the timeline it often stalls on the pieces of parallel audio I am describing. It goes silent and has to catch up and then plays. Would this be an issue with not a fast enough drive (to handle the picture and the audio  from another source and format) or a setting in the Programme, or a problem with doing what I am trying to do? 

Many thanks,

Elmer