Hi Sagar,
while I understand your issue this is imho a bad approach.
Besides the emulation workload you are also putting the full FW routing traffic between your subnets on the TE1000X.
Remember the TE1000X is running the FW blade hence it will check all traffic that is running through the gateway with it causing load.
The TE1000X will never be able to cope with the bandwith 2x 15000 can generate. The performance outcome is highly unpredictable.
Also your network design gets very complicated.
I would rather suggest trading in the NGTX license of your TE1000X and get a proper NGTX license on your GWs.
You won´t need NGTX on the TE1000X if you are not putting it inline or run MTA,ICAP,API services on the TE itself.
Regards Thomas