how can 5 goals get 15 points? if your use 1 a game over 5 games your drawing that's 10 points as you would of already had one point from the draw. You can't go from 0 points to 3 points in a single game with a single goal.
By using when you like so in the last 10 seconds of injury time safe to say 15 points
Now back to the question would be a different value to every club
The vast bunch of the league 15 points based on recent seasons won't be that valuable (might get you Europa League from mid table) but even that has a questionable value to premier league teams anyway
A team adrift at the bottom probably 50-75 million if it guaranteed survival
Just a quick bit of self-promotion, made my podcast debut on Gavins podcast going to be a weekly thing through the season with a couple more pre-season parts next week.