RSA still exist between these two trains.
1 yaer back before they used to have 3 3Ac coaches and 14 Sleeper.
As per 3 3AC coaches, Tatkal quota had 48 berths available in each train (16 berth per coach). Then simply B4 was attached to both the trains. Lower berth quota ( 2 berth per coach) became 8 berths in both the trains but Tatkal seats remained same (48 berths inspite of 4 3AC coaches).
Now...
more... in June ending this year, only for 12315/6, S14 was replaced by B5. This time, with increment of 1 bogie, 16 more berths were added to tatkal quota of 12315/6 making it to 64 berths. Also Lower berth quota was increased to 10 ( 5 coaches).
As per latest video of 12317/8, only 13 sleeper coaches are there and 6 AC coaches are there, but 12315/6 has 13 sleeper and 7 AC coaches.
At SDAH yard, they just add/remove the B5 coach. Thats why the rake of 12315/6 are never in same pattern. Sometimes B5 is just after B4, sometimes after A1 and sometimes after HA1. I travel frequently in this train so telling by experince.