Hi,
Do you see if the transfer progress? (snapmirror status -L on 7 mode, snapmirror show -instance on Cdot).
Is there any error messages on the relationships ? (i'ts common to have space/snap issues upon long lags) if it progresses - does it match the expected network disk/speed?.
If it's progress - but too slow. You can stop/quiesce some of the transfer and let the relationship to keep up one by one.
One reason I can think of with slowness is if the network routing has changed due to the failure. you didn't provide the ONTAP version, but most of them susceptible to fast-path route been removed or introduced when a secondary route being used on the other end. The first suspicion will be that the 100MB mgmt interface being utilized for the communication - check the different ports utilization to make sure it's as you expect it to be.