15W bayonet is the basic one for many very old and not that old (B15 socket, 15 millimeter diameter). It should fit, some have smaller sockets, mini size bulb, and there are all kinds.
I have bought this type of bulb for several of my machine, they have the same dimensions as the old ones. The tricky thing can be number of light diodes (the yellow square patches), the more there are of them the longer the bulb is. If the bulb points downwards, it can be an advantage to have have a few of the square patches on the end. If there's enough space in your machine you can experiement with higher wattage (longer bulb).