The Blockchaindriver has a bug. Open the AMD Settings and change that:

Make it to max and apply. Then start the miner. I use Cast XMR and my Vegas are between 1920-1960 H/s

i didn't install amd settings so I used that disable enable trick

i am using the xmr aeon stak version. not sure if that changes anything

https://github.com/IndeedMiners/xmr-aeon-stak/releases

I had the same Problem that i never used the AMD Software and my hashrate was just 1400 H/s. So I install it and it helped me a lot. Also i would try Cast XMR http://www.gandalph3000.com/download/cast_xmr-vega-win64_092.zip

the best i got with cast xmr stak was 1500+

Try Cast XMR and look for the Blockchaindriver bug and you get more then 1500 H/s