My DSL/Wi-Fi is extremely slow.

I'm having same problem too with my ipad 3.. i just can only connect to the wifi when my ipad stay next to router..

With that little amount of information, it will be difficult, if not impossible, to offer any type of help. All we can glean from your post is that you:

1. Have DSL service.
2. Have an 802.11ac AirPort Extreme base station, and
3. Have an iOS device, running v8.4.

What would help is if you tell us, at least, some of the following:

• What is the make & model of your DSL modem?
• Has this always been an issue or did this just start happening?
• What device, and operating system, will you be using to administer your Extreme with?
• When connected by Ethernet (assuming you have something other than an iPad, iPhone, or iPod Touch,) does the "speed" improve?
• Do you live in an environment that has numerous other Wi-Fi networks in operation? That is, in an apartment complex or dorm?

I have a Netgear model 6200 w/ 6.0 ATT DSL service

Ok, that Netgear is a combination modem & wireless router or gateway device. I am assuming that you have this configured as such and is working properly. Is the AirPort Extreme connected directly to the Netgear by wire or wireless? What is your networking goal for the Extreme? That is, are you trying to extend the Wi-Fi range of the Netgear or something else?

Coming out of the extreme w/ ethernet cable to a lighting adapter.

Sorry, but I'm not sure what you mean by a "lighting" adapter? Is this Ethernet cable connected to the Extreme's WAN (circle-of-dots) or one of its LAN (opposing arrows) ports? What is this adapter used for?

I live in a house w/ other wireless networks in the neighborhood.

Have you verified to see if your Netgear & Extreme routers are broadcasting on W-Fi channels that these other networks do not conflict with? You can use the built-in software on your iMac to do so.

Even when I run straight from the modem to the iMac it takes longer then usual to load.

Then your network troubleshooting should begin there. You should temporarily power-down the AirPort Extreme and work out why a direct connection to your Netgear gateway is not providing the data transfer rates that you are expecting. I suggest that you start by contacting your DSL provider and have them perform a "line check" to the gateway. Once they confirmed that it is performing correctly, then we can proceed with the next steps.