This is basically the reason why you have Music and Sound folders in C2. As you know both are just a sound files and can be treated same way (that's why it is possible to drag & drop them).
However Sounds are meant to be small. It is used for speciall effects, clicks etc. so usually sound is not longer than 3 seconds and very often it is less then a second. Such a short sound usually takes less then 50kB. So loading them at the start of the game shouldn't affect the overall loading time too much.
With music it is a bit different because music usually has several minutes, and that long sound files are already counted in MBs. So it affects the loading time.
Now when you have preloading sounds OFF, then the first time you sound will start it will be the time it gets loaded, so it might have a lag before it starts to play. So yes it is good to have it ON, because a game with laggy sounds is simply kind of frustrating.
In case that you have to move your music file to the sounds folder (this is a bug and will be fixed soon surely, but well if you have no choice at the moment let's focus on the currently possible solution) and it makes your game loading time too long you can try to load sounds manually.
So I would disable preload sounds in project settings, and load the sounds on your main screen in the background, to do so you simply use Audio object which has an action called "preload sound" or something like that (just from the top of my head).
Doing so your app loading time will stay normal. Your basic sounds/small sounds will load on main screen very fast. And while the game is on you don't have to preload music, simply start it.