Just to point out: a 20 min presentation would be max ten pp, times roman 12 font double space and a 30 min (which would be exceptionally long for a grad conf) is max 15 pp, NOT 15-20 pp.
People will get annoyed with you if you go over; the chair may cut you off in mid-sentence; do not try and read extra fast as no one will understand you anyway. and every topic is more complicated than you have time to lay out, which is why people write articles and books