How to reproduce:
1. Download and open attached project "WebClientTest"
2. Install and launch Wwise (added detailed steps how to install and setup Wwise in Edit)
3. Play the Scene in the Editor and observe the Console.

Expected result: Request times printed are between 15 and 50ms
Actual result: Request times printed are between 200 and 1500ms

Reproduced with: 2017.2.2p4, 2017.4.2f2
Cannot reproduce with: 2017.1.3p4 - cannot use function SendWebRequest(), 2018.1.0f2 and 2018.2.0b3 - no Wwise support for these versions.

Notes: WebClient hangs for ~1500ms and UnityWebRequest for ~200ms. The issue only reproduces on Windows. Tested requests with Fiddler shows 15 to 50ms result times.

Update:
After further investigation we have found out that *Wwise WAAPI is currently not supported feature for Unity*