I think we should consult an expert... that would be me.
do the math lol15,000 hours... hmmm...
none of us played that much ever, never came close actually. and here's proff:
Even if you play 6 hours a day, the whole year. you'll need to play 6 years and 10 months

And i don't think mastering the game requires 200m exp, i think 99 in all skills, and all quests is enough and lets say obtaining the most valued item. (so you can make anything and buy anything.)
I believe you can finish all quests in f2p (including the training for dragon slayer) in around 10-15 hours.
now for the skills, i get around 40K exp an hour in melee and im only level ~80 att-str-def, and even in that speed 99 in all three will only take 1K hours. (do the math)
you could get around 25-30K exp and hour powermining and powerfishing/cooking...
so getting 99 fishing, cooking, mining should take around 1.5K hours.
I made 50K firemaking exp in under an hour (around 75K exp fm an hour) meaning around 200-250 hours for 99 firemaking (considering you have the logs)
and you'll get the logs from 99 woodcutting. which will take around 300-350 hours (around 40K exp an hour)
i reach around 8-10K exp an hour rcing (earth runes w/ gloves) so around 1.2K-1.5K hours for that.
considering you work properly you can get close to 99 prayer using training and enough cash.
crafting can be as much as 60K exp an hour so 99 crafting should be around 250 hours.
count sadath was the closes so far, i suspect around 7.5-9K hours should do it

thing is none of you really understand how much time that is. even 7.5K hours = means 4 years and 2 months playing 5 hours ever day.