Just from a quick google search, it looks like it first came out in the 80s so it's definitely old school (assuming the mechanics haven't drastically changed in the editions since) but is it "OSR" feel/style in terms of the mechanics matching the tone?
It's definitely not OSR feeling, like I said it grew out of GURPS, so it's a lot more character customization focused, although it sidesteps the GURPS problem of having a million books by instead overloading the GM with the tools to write those books themselves. I just like the distribution skewing dice rolling mechanic.
Also, would 15 get you 5d6 instead (5x3=5)? Not to be pedantic but just making sure I understand the core mechanic.
Ah yes, I forgot to explain, you can always sacrifice a die to increase the bonus to +2, which is usually worth it. so if you have a 15, which would normally be 5d6, or even if you have 16 which would normally be 5d6+1, you can drop to 4d6+2, which mathematically is typically better. It's the only part of the mechanic that I'm not a fan of, because it makes gaining points suboptimal at times, since there's functionally no difference between having a 14 and 15, the difference between 15 and 16 is dubious, and your increase is really only indisputably better when you get all the way to 17. It's similar to post 3e attribute scores, where only even attribute points matters.