What Firmware version is currently loaded?
What is the Mfr and model# of the ISP modem the NG router is connected too?
What are your speeds UP and Down that you pay for?
What devices are you using to test speeds?
Be sure to test wired speeds along with wireless.
Try different devices to compare speeds.
What is the size of your home? Sq Ft?
What is the distance between the router and satellite(s)? 30 feet is recommended in between RBR and RBS to begin with depending upon building materials when wirelessly connected. https://kb.netgear.com/000036466/How-far-should-I-place-my-Orbi-satellite-from-my-Orbi-router
What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?
Try enabling Beamforming and MIMO(MIMO may or maynot be needed) and WMM. Under Advanced Tab/Advanced Settings/Wireless Settings
Try disabling the following and see:
Armor, Circle, Daisy Chain, Fast Roaming, IPv6 and Set 20/40Mhz Coexistence to 40Mhz only. Set Short preamble instead of Long preamble modes. Save settings and reboot the router and satellite(s).
Has a factory reset and setup from scratch been performed since last FW update?
