Yes, it is sound proof. STC Reference as follows:
34 - 38 Loud Speech Understood Schools
38 - 42 Normal Speech Audible; unintell Libraries, Churches
40 - 44 Loud Speech Audible, but unintell Meeting Rooms, Higher Ed
43 - 47 Loud Speech Barely Audible Boardroom, Clubs
46 - 50 Shouting Not Audible Community Halls, Private Meeting Rooms