How come Mr. Braun doesn't remember Suzuha?
As you pointed out, yes it is because of the name change. But let's look at the timeline of events after Suzuha  travels back to 1975 without changing the divergence ratio. 


1975: Suzuha Amane (19 years old) arrives in Tokyo but suffers amnesia.
1978: Yugo Tennouji (aka Mr. Braun) is born.
1999: Suzuha Amane (43 years old) remembers the events from before the time travel. In this time she helped Yugo Tennouji (aka Mr. Braun), who was 21 years old at that time, as Hashida Suzu. Suzuha Amane/Hashida Suzu suicides. 
2010: The 19 years old Suzuha Amane arrives in Tokyo and applies as a part-time worker at Yugo Tennouji (aka Mr. Braun) CRT store. Yugo Tennouji (aka Mr. Braun) is 32 years old in 2010.


So he only knew a 43 year-old friendly lady with the name Hashida Suzu who helped him 11 years before the events of D-Mail. It's not absurd that he doesn't connect her with a 19 year-old Suzuha Amane.

Source: Suzuha Amane Wiki, Yugo Tennouji Wiki