Creating a WorkFlow with mutiple conditions.

Hi, i am creating a workflow buy i think i doing something wrong.

There you can see an example what i’m doing:

Note: When it says -1 minute i will change it for -15 days.

The idea is the following:

When an account does not have activity for more than 15 days i want to create a task to the salesman in charge.

  1. I think that one way to do this is like the image. Multiple conditions including Tasks, Opportunities, Calls… and if the last modification date of all of them overpass the 15 days it triggers the action.

  2. Another way i think implies two workflows.
    The firstone consist in update the last modification date of the accounts when any activity is created or modify. So, for example if i create a task of account A at eleven o’clock, the last modofication date of the account will be eleven o’clock.
    The secondone prays: when the last modification date of the account overpass 15 days it’s trigger an action.
    I tried this way and the last modification date was updated succesfully, but i couldn’t trigger te action of the second workflow.

¿What do ypu think i should do? ¿where is my mistake?

Thanks in advance!