HERE is the key question: will you be by yourself? If you have a passenger, you can make use of the carpool lanes and save a bunch of time. Depending on back-ups at immigration checkpoint, your 90 minutes is quite realistic if you can use the carpool lanes, especially through El Toro and Santa Ana. I assume your destination is DL or is it somewhere else in Orange County?
Once you get past downtown San Diego and merge with the 805, you should start hitting some roads that will be moving well (at least until El Toro). If you want more info. about So. Calif. freeways, here it is: they are great at moving large amounts of cars. The trucks must stay in the right two lanes, but even they go pretty fast. If you are in the 3rd or 4th lane, make sure you aren't holding up cars behind you; if so, move over. When merging onto the freeways make sure you are up to freeway speeds!--this is an important safety tip. The road signs are large and clear. As far as traffic goes, it may be stop and go in places; if so, leave room in front of you and try to go at a consistent slow speed, rather than putting on your brakes constantly. Some freeway entrances have a stopligt system during high traffic periods. Read the sign-some say 2 cars per green. Others have a separate lane for carpoolers. Finally, gas is cheaper overall in Orange County than San Diego, but make sure you have enough to get there in one tank.
Last tip: if you have time, try to eat at In And Out Burger.