I don't want to generalize it but you could try tweaking below settings and see how much it can improve.
- Enable the OFDM.
- Set BSS min rate set to 12 Mbps.
- Enable band balancing and force clients to 5G radio.
- Disable overlapping channels on 2.4 G radio.
- Set channelization to 40 for 2.4 Radio and 80 for 5 Ghz (though it depends upon clien UE wireless capabilities what max speed it can achieve).
- Disable the self healing.
- Change scanning mechanism from channel fly to background scanning (set it to 600-1000 for 2.4 G and 600 for 5G).
- Enable 802.11N/AC only (Assuming that you don't have very old devices which only supports a/b/g and not n/ac).
- Set tx power to full (If it was modified to lower values manually).
Also I want to point that R510 APs can maximum support upto 867Mbps (if UE supports 802.11ac and connecting to 80MHz in ideal conditions).
Syamantak Omer | Community moderator | Staff TSE | CWNA | CCNA | RASZA | RICXI | Follow me at https://linkedin.com/in/syamantak-omer-5949b6124