Cisco ASA VPN – How to Keep an ASA Tunnel Up for Lifetime?

We have a Cisco ASA and at the remote end I have no idea what the device is. This is what happening:

When I send a packet or generate interesting traffic, it brings up the tunnel and everything starts working. The problem is that the remote end doesn't have an interesting traffic trigger and they won't be able to ping my machine until I send a packet and bring the tunnel up.

I did set SLA to generate interesting traffic but we have multiple subnets and every subnet creates its own tunnel.

This is what we have in the ACL at my side to generate interesting traffic:

Object group name - NET-REMOTE - 172.16.x.x/16

Here is the ACL:

access-list ACL-VPN extended permit ip 71.x.x.x 255.255.255.0 object-group NET-REMOTE
access-list ACL-VPN extended permit ip 61.x.x.x.x 255.255.254.0 object-group NET-REMOTE
access-list ACL-VPN extended permit ip 10.x.x.x 255.255.0.0 object-group NET-REMOTE

Here is the SLA statement:

sla monitor 10
 type echo protocol ipIcmpEcho 172.16.1.1 interface outside
 frequency 30

I can see that my isakmp policy lifetime is 86400 (24 Hours); but, still my tunnel is getting turned down in a few minutes:

crypto ikev1 policy 20
 authentication pre-share
 encryption 3des
 hash md5
 group 1
 lifetime 86400

At present, I have setup a continuous ping from one of my hosts to keep the tunnel up; but, this is not a good solution.

There must be a way to do this better.