Cablak,
Remember that you will only be able to control the traffic while it is on your equipment, once it leaves your network it is up to the ISP's to priorities the traffic how they want. You could police the traffic meaning when you are receiving traffic on the WAN when it is being placed into the buffers it would allow some types of traffic through with little to no buffer and buffer other traffic if needed due to the speed of the LAN, However usually the bandwidth coming in from the ISP in your case 6Mbps is much slower than the LAN at a minimum of 10Mbps usually 100 or 1000Mbps. There should be no reason why traffic is being held up getting onto your network.
The traffic going to the Internet you could QoS and shape the traffic as it leaves your network, for you 100Mbps to 1,5Mbps. You could give lets say voice traffic 512Kbps guaranty and the rest of the bandwidth to other forms of data, but you will need to do research on your traffic. If you set a protocols priority too low it might cause packet retransmission if it is TCP and cause more bandwidth being taken up vs less. Also if it is UDP traffic it might be dropped completly and stop working.
Make sure you are manually changing your Up and Down to match what you are getting from the ISP. Also remember if you priorities lets say voice over Data then you will see slower speed tests because you told it to.
I don't know your settings, or the type of traffic you have on your network, to know why you are seeing the results you are seeing but I hope this helps,
Cisco Small Business Support Center
Randy Manthey
CCNA, CCNA - Security
