Iceman has a lot of these - it seems like they all popped up in the last few years as he got older. We have had every one of them aspirated and they have all been fatty tumors, but I would rather let the vet tell me that than assume.
Having said that, if it isn't growing larger, I would wait until your appt in 2 weeks unless you see any changes. Hugs to you, I am sure it is just a fatty lipoma.