Kaz, many of us have bashed our heads trying to figure out these mystical "SA's"....and its about time Bort grants us a reset (when hell freezes over now appears to be the timeframe on that).
With regards to RR....I, and some others, believe that RR provides a FIXED bonus to speed/agility when running a route which is MOST beneficial to lower level characters.
Now there are many that LOVE and swear by this SA....the only thing that I can do is comment about it for my WR.
Take another look at the description on this SA carefully...(1) it states speed/agility bonus when running a route....in other words, after the route is done....bonus disappears and you are back to your natural speed/agility +equipment numbers. (2) see at bottom where it points out that the skill is important for receivers who are not otherwise very fast or agile...I believe the key lies within..stay with me here.
The two differing schools of thought out there argue these points. Some say they only want "ALWAYS ON" skills...they only want speed / agility since it does not need to TRIGGER and why waste points in SA RR that only pertains to running a route, may be fixed, and shuts OFF after route is completed.
The other school loves this SA and highly recommend it.
Me, I simply do not know
Say we have a level 20 WR with MADE UP NUMBERS as follows:
Speed and agility both at 30. If each level of RR provides a fixed bonus of ONE (1) to both speed/agil and we have 5 points in RR...this equates to a fixed bonus of 17% (5/30).
Later on, our WR is lucky enough to have 100 speed/agility with the same 5 points in RR resulting in a paltry bonus of 5%.
So, using your example of 15 in RR would result in massive bonus early on of 50% bonus to sp/agil while running a route vs. a mere 15% bonus to today (15/100). Granted 15% bonus is great but the cost was EXTREME to obtain.