At 24, I can confirm I hear the sound loud & clear, fairly close to the high pitch sound that regular (CRT based) television sets make. But then again, using a tone generator, I can hear up to about 18kHz. A TV produces a 15.6kHz (PAL) or 15.7kHz (NTSC) tone.
On the other hand, unless someone is aware that this is used as a ringtone, they would likely assume that it is something happening next door, particularly since it is quite difficult to tell the actual direction the sound is coming from. However, if a teacher can hear this sound and starts noticing students pulling out something everytime (s)he hears this sound, it will start becoming quite obvious what is happening.