More blocks with the same Model

So... If it's possible... How do i make it so i can make more blocks with the same custom model BUT have a different texture without making 14 more models and making each one of their texture mappings different and putting them on individual blocks?  For example, i was gonna make  vertical slab mod as a practice and i had to add 14 of the same .json but with different texture mappings and assign each vertical slab to each ones vertical slab. The problem is that it lags for a while everytime i change something or add something because it's checking all the models and stuff after a change.  PLEASE HELP it's getting on my nerves.