Hi Elena,
I am uncertain about if there is an given number of filters that would slow down the calculation of a smart list, but I do know if you are using a lot of contains/not contains and starts with/not starts with filters, this can sometimes slow down the time it takes for your smart list to generate. If you can, try using the exact values of the fields you are including in your smart list and utilize the is/is not filter.
Hope this helps!
-Val