Is my 15 month old sleeping too long?

My son is 15 months old. For the last 6 days he's had a cold with a runny nose and cough. For the last 5 days, he has slept excessively (like 15-18 hours a day) and he normally sleeps 13 or 14 max. He has also barely eaten anything. He will drink milk and maybe a couple blueberries or grapes and a cracker or two. Yesterday I was able to get about 3 oz of yogurt into him. I mean, I feel like he's probably losing wight at this point. It's almost 6 pm and he's on his third nap today and has been down since 3:30. He usually eats dinner at 5 and bedtime is at 7/7:30. Should I wake him up to try and feed him or just let him sleep as long as he needs since he is sick? By the way, he had his 15 month check-up yesterday and the doctor said his ears did look like there was fluid in them but since he had no fever and is sleeping well (past ear infections, he would rather scream than sleep!) that we should wait on antibiotics for now.