This sounds similar to what my 18 yr old cat had for the last 5 or so yrs of her life along with another larger one. When feeling the smaller ones they were hard and had kind of a “waxy” feel to them.
My vet in Philly said they were all from clogged up oil glands so essentially pimples or to be fancy with the larger one a sebacious cyst.
All anesthesia carries with it a degree of risk, however small, and it made no sense to put a cat that old thru anesthesia for what was basically a cosmetic issue. This was also a cat who had a lifelong congenital heart murmur.
But I have no way to know that it’s the same for your cat. I do like the previous suggestion to ask the vet to justify a reason for the biopsy. I would also get a second opinion perhaps from a local humane society which has vets on staff and are not necessarily so profit oriented and be more likely to give you an objective opinion.