I don’t know because I am still running 10.9 Mavericks and have no plans to “upgrade” any time soon. I did install the 2 newer OSs on a disposable disk but didn’t like the way they looked and all the fonts were hard to read. In any case, iTunes should be smart enough to degrade its font rendering despite not running the most modern OS. Even on my MBP with retina display it is hard to read.
The fonts looked good as of iTunes 11 when the font used was Lucida Grande, a much thicker and blacker font. In addition, the size adjuster in Preferences actually had some effect on font size and readability. With iTunes 11 Apple switched to Helvetica Neue which is thinner and greyer and hard to read. They also ruined the size adjuster which now has almost no effect. You could fix iTunes 11 easily by simply replacing all instances of “HelveticaNeue” with “LucidaGrande” in TextStyles.plist.
My hacking didn’t fix every problem. For example, this font is 3 or 4 points larger than original, but is still hard to read because Apple decided to break the cardinal rule of webmastering and put a black font on a green background:

If I get mad enough at it maybe I’ll try to hack it some more.