The 115 bit sets often are of lower quality.
I prefer to have brand name sets. . I have Norseman brand … set of standard, set of metric, set of letter, set of numbered (mostly very small sizes).
I think it was $450 well spent at the time. . Very useful when it comes to tapping, for one thing.
I tend to do a lot of "non-standard" things and for that, the large variety of drill bits is extremely valuable.
Rather than drill the instruction-sheet-recommended hole, I like to measure the tube and select my own drill bit to minimize the hole size that I drill.
That's what I do, altho' I know a lot of people would pooh-pooh that and say it is unnecessary.
The variety gives me flexibility to do unusual things and I have found this flexibility extremely useful, especially in my kitless activities.
You can minimize your $ outlay by buying individual bits as you need them, but who knows when you will need a particular size, or a "slightly-off" size to do a novel project that comes to you in the middle of the night. . On top of that, I think that the ultimate cost of acquiring a complete set through individual purchases would run you (at least) about 3x the price of buying the complete set at the beginning.