Financial planning for the next car

Hi, currently driving a Ford Focus bj2016 and would like to continue the compact class. The Focus cost new 15k and was financed to 60 months, with the financing with early replacement after 46 months was through. At that time I paid 300€ per month. So far so good, now I want to drive the Focus as long as it is economically worthwhile and ask myself how much money I would have to put aside to have enough money for an equivalent at the time of vehicle change. sounds hard to find, but I’m trying hard to figure out when the car will let me down. Currently it’s 70tkm of mileage after about 5 years. My plan would be to save 150€ per month from next year and replace the focus with 210tkm and 15 years old with the successor. Does that sound realistic? Or should I raise the amount? LG Haasinger