H1b 6 years calculation.Will it start from travel date with recent petition OR it calculate old petition stay date also

Hi,
Employer 1 applied fresh H1B for me. It was picked in lottery and got approved.
I was in USA from 15-Nov-2009 to 19-Sep-2010(308 days) from employer1
Again I was in USA from 29-May-2011 to 15-Dec-2012(566 days) from employer1.

Next I joined Employer 2 and Employer 2 applied fresh H1B for me. It was picked in lottery and got approved.
With that H1B I stayed in USA from 15th Feb’2015 to till date.Now my current H1b petition is approved up to 23 rd Sep’2017.

What my understanding is as Employer 2 had applied fresh H1b and I had more than 2 + years gap between last stay from Employer 1(15-Dec-2012) and my current stay start date(15-Feb-2015) ,my H1b 6 years cycle should start from 15-Feb-2015.

My question is what will be the 6 years duration up to that date I am eligible to stay at US??

Will it start from 15th Feb’2015
OR
my earlier stay before 2015 also will be calculated.

Please provide your suggestion. Appreciate your help.