Thats not how it works. Ability to carry them is enough to add them and as we see there is ability of it.
That’s how balance works. There is enormous amount of vehicles that don’t have everything that they are capable to carry for balance reasons. Doing the same with Su-15 is only fair to not put it at too high of a br
I dont think that plane with 4x R-60 and two medium range missiles should be too low in BR. MiG-21SMT for example is on BR 10.3 with 4x R-60. I think that Su-15TM will go on BR 10.7 where are flares quite a necessity. And since it carried them irl, it should get them in the game too.
Su-15 is not MiG-21 levels of flight performance tho. If it was like MiG-21SMT - sure thing, give it flares and put it at 10.7. Another thing is that Su-15s never used double R-60 pylons

Here you go.
Flight performance can be worse but armament is much better than on SMT.
hmmm Su-15TM can carry also UB-32.

Су- 15TM №10-07 с подвешенными УПК-23-250 и блоками УБ-32. Испытания по «фронтовому применению». Владимировка, 1975 г.
The issues with the flares is that you have to trade them for the gun pods, so the 10.3 should be fine, or allow it to carry both and put it at 10.7, although not sure if thats even possible
Its not…you can use flares or gunpods.
Then 10.7 is likely too high for it
Maybe 10.3. Depends on how powerful will be R-98M. Still should have option for flares.
Aside from the range is there any info about the seeker of the r98M, are they pulse or CW?
Then they will be no better than the r3r, aside from some extra range, also quite a weird redaction as they start talking midway about the r23 seeker on the r98m section
What I readed in forum section:
14G limit. Idk if its correct but if it is so then should be little bit better than R-3R.
Not sure about the 14g, he also gives it target overload of 3g instead of thr 2g from source that you attached
It would be ideal if we had some kind of operating manual for this.
I mean being only operated by the PVO probably doesnt help with that
I rather have it with 2 R-60 and no flares at 9.7 than with 4 R-60Ms and flares at 10.7
Me personally I would rather have one on higher BR with whole armament but we can have more variants. For example Su-15T on BR 9.7 and Su-15TM on BR 10.3/10.7 (depending on how it will works).