Top 20 is quite high, even with a forward heavy top 20 (of say 13 of them) even harder with a more balanced 10-12 forward in the top 20,
Many of those 10:
Gretzky
Howe
Lemieux
Beliveau
Hull
Richard
Morenz
Mikita
Messier
Clarke
Are hard to get above, then you have Jagr/Sakic/Yzerman/Lafleur/Esposito/Trottier/Bossy
And the new competition Crosby, Ovechkin, McDavid that could be one by that time.
Because he missed a lot of game he only has been 4 time in the league top 10 scorer, Jagr/Crosby/Sakic/Esposito did it 10 time or more Ovechkin could achieve that also, that will probably hurt him quite a bit like for Forsberg.
His playoff resume could end up above average in the group fighting for those last place at least, but it is not like many of them do not have a really strong one.
Top 15 sound really hard, even if you push it with 10 forward in your top 15 (with just Orr, Hasek, Roy, Bourque, Harvey, you need to remove 4 in that list for him
Gretzky
Howe
Lemieux
Beliveau
Hull
Richard
Mikita
Messier
Clarke
Crosby
Ovechkin
Jagr
Morenz
The league will over 100 year's old when he will retire, having Lidstrom, Brodeur, Crosby, Ovechkin from the 25 year's before in the league history top players (maybe McDavid) will make it hard to squeeze many other names, he will be in those conversation for sure too and still many games to be played for things to change.