Thanks, tinismom, that's an idea we hadn't thought of! We use the Tommee Tippee bottles and the slowest nipple they have, stage 1.
Lilpats-mama, its good to hear someone else's experience at the same age! I'm really hoping he doesn't need 15 oz all the time, but I'll keep it in mind that he might. I'd rather increase solids and get his nursing in when I'm there, though.
Today did seem to go better. He was less fussy, and DH thought maybe he'd been a little under the weather the past 2 days and that's why he was hungrier. Today he took 12 oz, which is closer to what I think he should.
Either way I will add another pumping session at work. That will make 4 pumping sessions in a 9-hour day. I'm sure my boss thinks I'm just always pumping and never working (and it feels like it to me too), but I couldn't give up any more sleep to pump at night! (DS still nurses every 2-3 hours at night anyway.)