Here's my take on it:
If you can, change your home network scheme to 192.168.64.x/24 or something higher than a value of 63 in the third octet. That way, you could create one ipsec vpn tunnel and run a parallel vpn design. Say you chose 192.168.75.0/24, you could use the following scheme:
From your home to the office:
Local: 192.168.75.0/24
Remote: 192.168.0.0/18
Of course, from the other end, you will reverse the groups and it should work just fine when you create the respective rules on the office side to allow entry into the different work subnets.
In case you have your 15 subnets ranging all over the place, change your home ip scheme to something either in the 172.16.x.x range or the 10.x.x.x range. With that done, make the respective changes to your IPSEC vpn and you should be fine with the one IPSEC vpn tunnel.
Enjoy and good luck!
Good luck!