Upgrade the Omicron Pilot to Captain Yorr, since he'll be able to pull the stress tokens away from your Interceptors.
I'm not sure I agree with this, not because pulling stress off Interceptors isn't awesome, but because of the range fo this ability. Interceptors are dogfighters. They excel at getting behind enemies and hounding them with ferocious fire. Hard turns, aggressive tactics, and fancy flying are where these craft excel.
On the other hand, the winter void moose is best at boom and zoom. This venerable beast should move rapidly into combat, then move slowly for several turns until it starts losing shields or the combat passes it, then zoom off, escape combat distance, and turn to begin another pass.
The problem with Yorr's ability is it ties these two craft together. You either have to accellerate your albino space rhebok into combat, crippling its ability to turn with the combat and maintain heavy fire, then hitting it with stress so it can't pull one of its infamous escapes, or you keep a tight leash on your interceptors, keeping them in enemy fire arc longer and limiting their movement options.
No, if you are going to pump 3 points into the Shuttle, upgrading to Yorr is not the way to do it with this list. My recommendation is Rebel Captive. This is a terrible upgrade for your enemy to face. It gives a craft that fires on your shuttle a stress token, which vastly limits that craft's ability to maneuver, which is lethal with interceptors around. Further, it may make your enemy disinclined to attack the shuttle, forcing them to attempt to engage your Interceptors while suffering withering fire from a target they don't want to attack.
Come down to Sable's Shuttle Emporium for all your Alabaster Void Bison needs!
Empire: 5 TIE Advanced, 5 TIE Bombers, 8 TIE Fighters, 2 TIE Interceptors, 4 Firespray-31s, 4 Lambda Shuttles
Rebel: 5 A-Wings, 5 B-Wings, 4 X-Wings, 4 Y-Wings, 4 HWK-290s, 2 YT-1300s