How much time does one need to save 13.5k ?

I've been playing eFootball for around 1.5 years, so I'm definitely not a new player. I've seen people talk about the 13.5k coin strategy quite a lot, but I never really paid much attention to it because it always felt like such a long-term commitment.

However, I seriously regretted that decision when I missed the Patrick Vieira pack. I'm mostly F2P, and since I'm a student, spending money on the game is something I have to be very careful about. I did around 110 spins on that pack without getting anything at all. At that point, I seriously considered recharging, but ultimately decided against it because of my financial situation.

That experience made me rethink how I manage my coins. Now I'm wondering: if I start saving seriously, how long would it realistically take to reach 13,500 coins as a F2P ?