High latency after wan failover configuration

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i running pfsense 2.1.5
I create wan fail over 
I used this guide
Youtube Video

and it is work

but I have a small problem
the latency Has become very high

Usually it is Between 7 to 15
after wan failover configuration it is Between 70 to 150

So I deleted the settings of wan failover
And went back to Standard setting

then the  latency back to be Between 7 to 15

This is supposed to happen or I do something wrong ?
why the latency go high when there is wan fail over ?