Reduce categories (more than 3 millions)

[Manteka20]

Hi, i have a website of spare parts

The users access each car model by the top block menu, then the page presenting the type of part for that model

we have several car types -  Example:

VW -

Mk1 Golf

Mk2 Golf

Mk3 golf

Etc

 

Audi

A3 Mk1

A3 Mk2

 

SEAT

Leon Mk1

Leon Mk2

 

inside each type  of car you have the type of parts - Example:

Bushes

Exhausts

Air filters

Springs

Styling

Etc
 

Actually we have more than 3 millions of categories,,,, how we can reduce categories????