I would definitely recommend upgrading to 2.9.0. You will have to upgrade to 2.6.2 first, and then to 2.9.0.HA (you do not have to upgrade AP firmware in this manner though - you can upgrade it straight to 2.9.0). Please see BlueSocket/vWLAN Version 2.9.0.HA Released for more information. 2.9.0 does have a few optimizations for the 1800v2s, but remember being EOL there are hardware limitations in conjunction with new client wireless chips.
Another good idea is to make sure you have smaller coverage cells and a good site channel/power plan so that clients are more evenly distributed. The less clients on the radio, the less strain on your 1800s. You can also use the vWLAN configuration to limit the number of clients per radio as well.
You can use Avoiding RF Interference with a Successful BlueSocket Wireless Deployment for more information on proper channel and power settings.
ADTRAN Product Support Engineer
I would also suggest you give your local ADTRAN sales rep or partner a call. We have a promo going on where you can trade up to 11ac at significant discounts.
After two months of work vWLAN 2.9.0HA, we have problems:
1) random AP lost connection with vWLAN
2) 2.4G radio down - with no error message on vWLAN
3) AP goes into a cyclic reboot, after the setup 5G U-NII-2A
Now we try 3.0.1, after 2 days showing clients information bugly
1) Searching not working
2) Sorting not working