Converting date formats

I received a .csv file and the date format in the file is:

2015-05-11-02.59.58.878520

When I import the data into Power BI, it imports the date as a string and all attempts at converting this string to a date format has failed.  I added a new column and used both these formulas

 =DATEVALUE("2015-01-26-02.59.33.625380") 

Measure = DATEVALUE(LEFT("2015-01-26 02.59.33.625380",10)) 

Please help?  I need all the decimals as I am doing a SLA analysis where I need to calculate the time lapsed between records.

Thanks so much in advance