Yes, Otay is faster.
But figure it takes about 20 minutes to go the Otay gate from downtown TJ and 10 minutes to go from the Otay gate to I-805. So you have to save more than 30 minutes to justify crossing at Otay. (Which is usually the case on Sundays.)
The best time to cross at either gate is between 1:30 am and 2:30 am. You should be able to see why without an explanation. "Workers hours" start soon after 2:30 am.
The worst time to cross is about 6-9 am, when many, many people cross to work in the US. Weekends also are bad, with Sunday being worse than Saturday.
Among the times most tourists cross Tuesday, Wednesday, and Thursday evenings and nights are the best at both gates.
You can get crossing time estimates (usually about 25% overly optimistic) by calling:
664-700-7000 - Otay and San Ysidro
619-671-8999 - Otay Gate
619-690-8999 - San Ysidro Gate