I was troubleshooting slow (~<4Mbps) downloads on my new phone and discovered that increasing the hw retries setting allowed it to get good (~20Mbps) speeds. I also noticed in the Wireless FAQ it says that setting a value, “going below 2 is not reasonable in most cases,” but the default is set to 0. Just wanted to let others know in case this issue comes up again. I posted this also on the reddit page for these phones. I did some testing with different hw retries values from 3-15 and they all seem to provide the same speed, so I left it set to 5. Thanks, Mikrotik!
https://www.reddit.com/r/zenfone2/comments/3xdgxj/fixed_slow_wifi_4mbps_via_mikrotik_rb951g2hnd_on/