I save my recordings as I go along as .aup, the native Audacity file type. This is so fast (a contrl+s) I can save every time I stop for anything thus my save file is almost always up to date and if an electrical outage occurs, nothing is lost.
When opening an .aup file that has been closed, it opens significantly more quickly for me than an MP3. it is my belief that the .aup files are a form of losless data storage but I have no proof of this. So working with the .aup file, editing, making changes, etc. seems to avoid the lag and stuttering that I've experienced when opening and working with MP3 files. Not often, but it has happened. Only when the file is completely edited and ready for export do I make an MP3.
yeah, I know this is not the normal procedure for most people who save FLAC and are more cautious but I have never lost any .aup files (except for the time I stored it in the wrong place and it took a week to find it) and they just seem so much quicker to work with that it is my normal procedure. Of course the .aup file has two parts, the .aup and the data file which must be in the same folder. This is automatic but if you should move one, it won't be found until you move them both into the same folder. Long post to just suggest working with .aup and see if it loads more quickly.