Criteria of experience recognition for "TV-L 13" position
Since universities are governed by state law, it matters which state this is in. In general, you should be hired at Stufe 2 if 


you have been employed (i.e., not receiving a stipend or contracted to provide a specific service)
for at least a full year (this can be on multiple contracts, though)
in a similar capacity as the position for which you are to be hired (i.e., after your PhD at a German university, research institute, or comparable institution)
within 18 months (i.e., there should not have been a cumulated break of more than 18 months between these employments, including ineligible forms such as stipends and service contracts).


(If you have more than three years of eligible employment, you are entitled to Stufe 3, but that is usually hard to get.)

Things are a bit more complicated since there is a wider catalog of förderliche Zeiten ("beneficial time") which the university may recognize (but usually don't to save money, sometimes categorically as in Berlin). This includes the more prestigious stipends or scholarships such as DAAD or Humboldt fellowships. This is not something you can argue for, though, but the hiring person needs to apply for with the administration if they believe they have to offer it in order to attract a specific desirable candidate.