Your router was an entry level one 10 years ago, with an underpowered cpu which may not be able to the packet forwarding.
If your devices are.on WIFI it cpuld simply be interference from other devices limiting your speeds. Plug the scanner (and ideally target pc) into ethernet to allow better use of yhe limited wifi spectrum. If tjis cant work, move scanner closer to pc for a minor improvement, or get a decent model router that supports 802.11AC and make.use.of AcC (ie 5 gig band) where possible.
If your devices are already plugged in via ethernet - Find a very cheap switch and plug all the devices into that and then cable the switch to a router LAN port such that the router only has 1 cable in the LAN, this will take the switching load off the router. Replacing tje router is also not a bad option.
I also note that dd-wrt might be an option on your router and can often help, and do things like QoS - if your time is worth less then the value of a replacement router, and you can try getting a boost by installing it - https://wiki.dd-wrt.com/wiki/index.php/Netgear_WNR2000v3 (but on a constrained 10 year old router I probably wouldnt bother)