delays with L2L VPN when applying encryption

[k.abillama]

I have a setup where L2L IPSEC tunnel is established between two routers. The problem is that when we apply encryption, there is a very high increase in the delay between the two sites. Please advise what could possibly be the problem knowing that I already did the below without success:

- Changed the hash and encryption algorithms

- Modified the mtu with the TCP-MSS-adjust command

[Collin Clark]

What model are the routers? Do they have the AIM encryption module installed? What are the resource being used w/o VPN? Then with VPN?

[k.abillama]

Hi, the HQ router is a 3845 router running IOS c3845-advsecurityk9-mz.124-15.T7.bin without AIM module and the branch router is a 2811 router running IOS c2800nm-advsecurityk9-mz.124-15.T7.bin without AIM also.

The tests being used are mainly file transfers and icmp echoes as well