Q:

AlwaysOn Async read takes more time when compared to that of Sync secondary

AlwaysOn Async read takes more time when compared to that of Sync secondary (by a small fraction).  Is this expected behaviour?  I was under the impression that ASYNC must be faster than the SYNC. 

A:

There are a number of different factors involved but it is entirely possible to have a replica that is synchronous be faster or slower than an asynchronous one. 
To list a few:

Replica is under too much load
Hardware specification differences (i.e. synch runs ssd and async runs rotational) or synch is using 8 cores @ 3.6 GHz and async is using 4 cores @ 2.4 GHz
Stats and/or indexes were updated and haven't yet been fully redone on the async
Geographical network latency

