His heart always seems fine on checkups. Don't know how fast the condition starts though. Read a post about a Chihuahua that had similar issues. Coughing leading to not being able to breath. Calling vet today.
Congestive Heart Failure????
I don't have any good advice, but wish you luck. Our dog is 15 also, and it really scares you when there is any changes in them, I would call the vet, hopefully it is something simple like an ear infection that can be treated with antibiotics.
He gets yearly checkups. All good. Takes arthritis meds for his legs and a pain pill once in awhile. Have not gone to the vet since this started. Figured when my time comes I don't want doctors prodding me, wanted to give him the same respect. Might have to call vet though.
15 is an advanced age for any breed - has your dog had a full physical exam by a vet in the past 12 months? If not that alone is a reason, and given the symptoms you have two reasons to take your dog to a vet.