I recently upgraded my internet which is advertised to be "5.0 to 25.0 Mbps Download speed" and "Up to 2.5 Mbps Upload speed". After my supposed upgrade I tested my speed on speedtest.net and didn't notice any difference from what I had before. This morning I set about diagnosing where in my network this comes from. At my ISP modem I get the advertised speeds, and before my home WAN/LAN router I get those speeds, but my router seems to be stuck at 15Mbps/1Mbps. It is a fairly old router a "phased out" dlink DIR-615. The specs say that the router has 4 10/100 LAN Ports. What does the "10/100" mean? and do I need to upgrade my router?
The "10/100" means the ports are 10/100Mbps ports (Megabits Per Second), meaning they'll negotiate at either 10Mbps or 100Mbps, depending on the device attached to the port.
As for your speed differences, it may just be that that router can't route that fast, and you may be out of luck until you get a newer, more capable router.
But there have been reports that changing the WAN port speed to 100Mbps instead of leaving it on "Auto" may help it negotiate speeds with certain modems properly, giving full speed.
The WAN port speed should be adjustable in the "Advanced Network Settings" menu of the router.