Sounds about right. Current race lap records at MRLS:

ITR 1:43.359 77.94 JOSH SIROTA CUPERTINO, CA 99 BMW 5/4/2008
ITS 1:43.224 78.05 DOUG MAKISHIMA DUBLIN, CA 87 BMW 10/27/2007
STL 1:43.488 77.85 Lucas Catania 2013 Mazda MX-5 3/30/2014
STO 1:32.924 86.70 STEVE GOLDMAN MALIBU, CA 08 PORSCHE 6/21/2009
STU 1:37.811 82.37 Andrie Hartanto Concord CA, CA 2005 Honda S2000 6/7/2014

1:43.3 to 1:37.8 -> 4.5 seconds

IT's not been doing so well down here, and I can't say how it's doing in SFR, but based on this year there's 3 ITS cars and 1 ITR car at the last divisional at Sears Point.