VPN Through put Slow

Hi All,

we have configured IPSec on m0n0wall on our Head office and on one of our
branch, There is a webserver at our head office behind m0n0wall now the
question is that when we access webserver with Public IP from branch office
it connected very quickly but when we try to connect via local ip throught
IPSec than it takes much time can anybody tell me why??

here is the configuration of IPSec

Negotiation mode : Aggressive
Encryption Algorithm : 3DES ( Also Tried with Blowfish at both end as we
read somewhere that its recommmended)
Hash Algorithm : SHA1
DHKey Group : 2
Authentication mode : Pre shared Key
Protocol : ESP

Sajjad