Q:

Carrying remote VLAN via 2 routers to the local gateway

I have a serverA (192.168.15.1) from site A and VLAN is 15, however the VLAN 15 gateway is set at site B (192.168.15.254). 
There are two ISP routers as a metro role to connect each other by subnet 10.0.0.0/30. 
My question is how can I get past those two routers? Could any one give an example to accomplish this? Thanks.

PS. I can ping from serverA (192.168.15.1) to an interface f0/0@R1(10.0.0.1), no more further. 

A:

You can use Ether in IP, defined in RFC 3398 to tunnel ethernet through IP, if you equipment supports it.  It's similar to the VxLAN approach, but a little simpler and older.
If you don't have those and it's desperate, you could think about proxy ARP.  It is really not recommended.

Do you have a particular reason to bridge like this?
I'd suggest you strongly consider renumbering so you can just use ordinary IP routes.  Perhaps you are nearly there already, if 192.168.15.0/25 is left and 192.168.15.128/25 is right?  Renumbering R1 f0/1 (.126?), change masks, add routes to R1 and R2.

A:

You can use VxLAN, defined in RFC7348, to span a VLAN onto different sites.
Basically it encapsulates a VLAN into IP.
This off course add some overhead, and your routers at each endpoint need to support VxLAN

