Is 15 plates car battery good? Yes, if it is the same or better than the original battery fitted by the car maker. You can use this size of battery for cars with large petrol engines, most saloon vehicles and most petrol engine SUVs. You can also install a 15 plates battery for diesel engine saloon vehicles.
There are many exceptions to this, e.g. Honda Civic, Honda CRV, Toyota Yaris. These car manufacturers design the battery compartment for smaller batteries. Their original batteries are in the 13 plates and 11 plates range. Don’t feel pressured or scared into changing to a larger size battery.