High calcium and weight loss in elderly cat?

My cat is fourteen, will be fifteen in February.

He has lost weight over the last year or two. We went to the vet in December and his calcium was slightly elevated. We went back this week and his calcium has gone up and he has lost another pound or so. The vet said the next step would be an ultrasound to diagnose cancer and potentially give him chemo pills. My thoughts are...he is fourteen. I am not going to drag him through chemopills and drawn out treatment and potentially pain and discomfort just so I can can have more time with him. If it's his time to go, I want him to have the best last months he can and let him go before he suffers.

The ultrasound is about 800 dollars (the cheapest I could find at a certified vet). While it won't be devastating for me to pay that, I have several other expenses coming up as well and it is a lot all at once. The vet stated that if I choose to not do the ultrasound, we can start him on Prednisone to potentially slow cancer/treat potential IBS. I'm leaning toward just doing the steroids and monitoring his progress. But it's just such a hard decision. I just don't want him to suffer.