Thank you guys, got it working with your help
I have 4 x 4-digits displays, with daisy chained 595 chips driving their segments. so I need only 3 arduino pins for segments, which is great, but I still have the digits wired directly to the arduino taking 16 pins.
That's the part I would like to improve now, I want to handle digits them the same way than segments, through the same IC, but my doubt is about the extra time that would take in the loop.
Will I be able to refresh the displays on time without flickering or any other issue?